diff --git a/client/src/main/java/org/asynchttpclient/AsyncCompletionHandler.java b/client/src/main/java/org/asynchttpclient/AsyncCompletionHandler.java
index fe193d37f..e5cb67207 100644
--- a/client/src/main/java/org/asynchttpclient/AsyncCompletionHandler.java
+++ b/client/src/main/java/org/asynchttpclient/AsyncCompletionHandler.java
@@ -18,6 +18,7 @@
 
 import io.netty.handler.codec.http.HttpHeaders;
 import org.asynchttpclient.handler.ProgressAsyncHandler;
+import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -66,7 +67,7 @@ public State onTrailingHeadersReceived(HttpHeaders headers) throws Exception {
     }
 
     @Override
-    public final T onCompleted() throws Exception {
+    public final @Nullable T onCompleted() throws Exception {
         return onCompleted(builder.build());
     }
 
@@ -83,7 +84,7 @@ public void onThrowable(Throwable t) {
      * {@link Future}
      * @throws Exception if something wrong happens
      */
-    public abstract T onCompleted(Response response) throws Exception;
+    public abstract @Nullable T onCompleted(@Nullable Response response) throws Exception;
 
     /**
      * Invoked when the HTTP headers have been fully written on the I/O socket.
diff --git a/client/src/main/java/org/asynchttpclient/AsyncCompletionHandlerBase.java b/client/src/main/java/org/asynchttpclient/AsyncCompletionHandlerBase.java
index 3498bd643..8ad58eff6 100644
--- a/client/src/main/java/org/asynchttpclient/AsyncCompletionHandlerBase.java
+++ b/client/src/main/java/org/asynchttpclient/AsyncCompletionHandlerBase.java
@@ -17,12 +17,14 @@
 package org.asynchttpclient;
 
 
+import org.jetbrains.annotations.Nullable;
+
 /**
  * Simple {@link AsyncHandler} of type {@link Response}
  */
 public class AsyncCompletionHandlerBase extends AsyncCompletionHandler<Response> {
     @Override
-    public Response onCompleted(Response response) throws Exception {
+    public @Nullable Response onCompleted(@Nullable Response response) throws Exception {
         return response;
     }
 }
diff --git a/client/src/main/java/org/asynchttpclient/AsyncHandler.java b/client/src/main/java/org/asynchttpclient/AsyncHandler.java
index 80a1fc191..74099cc4d 100644
--- a/client/src/main/java/org/asynchttpclient/AsyncHandler.java
+++ b/client/src/main/java/org/asynchttpclient/AsyncHandler.java
@@ -18,6 +18,7 @@
 import io.netty.channel.Channel;
 import io.netty.handler.codec.http.HttpHeaders;
 import org.asynchttpclient.netty.request.NettyRequest;
+import org.jetbrains.annotations.Nullable;
 
 import javax.net.ssl.SSLSession;
 import java.net.InetSocketAddress;
@@ -115,7 +116,7 @@ default State onTrailingHeadersReceived(HttpHeaders headers) throws Exception {
      * @return T Value that will be returned by the associated {@link Future}
      * @throws Exception if something wrong happens
      */
-    T onCompleted() throws Exception;
+    @Nullable T onCompleted() throws Exception;
 
     /**
      * Notify the callback before hostname resolution
diff --git a/client/src/main/java/org/asynchttpclient/AsyncHttpClientConfig.java b/client/src/main/java/org/asynchttpclient/AsyncHttpClientConfig.java
index 1c5ab1b5a..972fa0b3a 100644
--- a/client/src/main/java/org/asynchttpclient/AsyncHttpClientConfig.java
+++ b/client/src/main/java/org/asynchttpclient/AsyncHttpClientConfig.java
@@ -34,6 +34,7 @@
 import org.asynchttpclient.netty.channel.ConnectionSemaphoreFactory;
 import org.asynchttpclient.proxy.ProxyServer;
 import org.asynchttpclient.proxy.ProxyServerSelector;
+import org.jetbrains.annotations.Nullable;
 
 import java.io.IOException;
 import java.time.Duration;
@@ -159,7 +160,7 @@ public interface AsyncHttpClientConfig {
      * @return the {@link ThreadFactory} an {@link AsyncHttpClient} use for handling asynchronous response. If no {@link ThreadFactory} has been explicitly
      * provided, this method will return {@code null}
      */
-    ThreadFactory getThreadFactory();
+    @Nullable ThreadFactory getThreadFactory();
 
     /**
      * An instance of {@link ProxyServer} used by an {@link AsyncHttpClient}
@@ -173,14 +174,14 @@ public interface AsyncHttpClientConfig {
      *
      * @return an instance of {@link SslContext} used for SSL connection.
      */
-    SslContext getSslContext();
+    @Nullable SslContext getSslContext();
 
     /**
      * Return the current {@link Realm}
      *
      * @return the current {@link Realm}
      */
-    Realm getRealm();
+    @Nullable Realm getRealm();
 
     /**
      * Return the list of {@link RequestFilter}
@@ -259,12 +260,12 @@ public interface AsyncHttpClientConfig {
     /**
      * @return the array of enabled protocols
      */
-    String[] getEnabledProtocols();
+    @Nullable String[] getEnabledProtocols();
 
     /**
      * @return the array of enabled cipher suites
      */
-    String[] getEnabledCipherSuites();
+    @Nullable String[] getEnabledCipherSuites();
 
     /**
      * @return if insecure cipher suites must be filtered out (only used when not explicitly passing enabled cipher suites)
@@ -293,7 +294,7 @@ public interface AsyncHttpClientConfig {
 
     int getHandshakeTimeout();
 
-    SslEngineFactory getSslEngineFactory();
+    @Nullable SslEngineFactory getSslEngineFactory();
 
     int getChunkedFileChunkSize();
 
@@ -309,23 +310,23 @@ public interface AsyncHttpClientConfig {
 
     Map<ChannelOption<Object>, Object> getChannelOptions();
 
-    EventLoopGroup getEventLoopGroup();
+    @Nullable EventLoopGroup getEventLoopGroup();
 
     boolean isUseNativeTransport();
 
     boolean isUseOnlyEpollNativeTransport();
 
-    Consumer<Channel> getHttpAdditionalChannelInitializer();
+    @Nullable Consumer<Channel> getHttpAdditionalChannelInitializer();
 
-    Consumer<Channel> getWsAdditionalChannelInitializer();
+    @Nullable Consumer<Channel> getWsAdditionalChannelInitializer();
 
     ResponseBodyPartFactory getResponseBodyPartFactory();
 
-    ChannelPool getChannelPool();
+    @Nullable ChannelPool getChannelPool();
 
-    ConnectionSemaphoreFactory getConnectionSemaphoreFactory();
+    @Nullable ConnectionSemaphoreFactory getConnectionSemaphoreFactory();
 
-    Timer getNettyTimer();
+    @Nullable Timer getNettyTimer();
 
     /**
      * @return the duration between tick of {@link HashedWheelTimer}
@@ -357,7 +358,7 @@ public interface AsyncHttpClientConfig {
 
     int getSoRcvBuf();
 
-    ByteBufAllocator getAllocator();
+    @Nullable ByteBufAllocator getAllocator();
 
     int getIoThreadsCount();
 
diff --git a/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClient.java b/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClient.java
index efcab12a9..ab841fa28 100644
--- a/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClient.java
+++ b/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClient.java
@@ -30,6 +30,7 @@
 import org.asynchttpclient.handler.resumable.ResumableAsyncHandler;
 import org.asynchttpclient.netty.channel.ChannelManager;
 import org.asynchttpclient.netty.request.NettyRequestSender;
+import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -68,7 +69,7 @@ public class DefaultAsyncHttpClient implements AsyncHttpClient {
      * Default signature calculator to use for all requests constructed by this
      * client instance.
      */
-    private SignatureCalculator signatureCalculator;
+    private @Nullable SignatureCalculator signatureCalculator;
 
     /**
      * Create a new HTTP Asynchronous Client using the default
@@ -95,8 +96,14 @@ public DefaultAsyncHttpClient(AsyncHttpClientConfig config) {
 
         this.config = config;
         noRequestFilters = config.getRequestFilters().isEmpty();
-        allowStopNettyTimer = config.getNettyTimer() == null;
-        nettyTimer = allowStopNettyTimer ? newNettyTimer(config) : config.getNettyTimer();
+        final Timer configTimer = config.getNettyTimer();
+        if (configTimer == null) {
+            allowStopNettyTimer = true;
+            nettyTimer = newNettyTimer(config);
+        } else {
+            allowStopNettyTimer = false;
+            nettyTimer = configTimer;
+        }
 
         channelManager = new ChannelManager(config, nettyTimer);
         requestSender = new NettyRequestSender(config, channelManager, nettyTimer, new AsyncHttpClientState(closed));
diff --git a/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClientConfig.java b/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClientConfig.java
index 9dfaa89f4..059cc3e78 100644
--- a/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClientConfig.java
+++ b/client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClientConfig.java
@@ -34,6 +34,7 @@
 import org.asynchttpclient.proxy.ProxyServer;
 import org.asynchttpclient.proxy.ProxyServerSelector;
 import org.asynchttpclient.util.ProxyUtils;
+import org.jetbrains.annotations.Nullable;
 
 import java.time.Duration;
 import java.util.Collections;
@@ -44,7 +45,63 @@
 import java.util.concurrent.ThreadFactory;
 import java.util.function.Consumer;
 
-import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.*;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultAcquireFreeChannelTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultAggregateWebSocketFrameFragments;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultChunkedFileChunkSize;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultCompressionEnforced;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultConnectTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultConnectionPoolCleanerPeriod;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultConnectionTtl;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultDisableHttpsEndpointIdentificationAlgorithm;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultDisableUrlEncodingForBoundRequests;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultDisableZeroCopy;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultEnableAutomaticDecompression;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultEnableWebSocketCompression;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultEnabledCipherSuites;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultEnabledProtocols;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultExpiredCookieEvictionDelay;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultFilterInsecureCipherSuites;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultFollowRedirect;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultHandshakeTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultHashedWheelTimerSize;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultHashedWheelTimerTickDuration;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultHttpClientCodecInitialBufferSize;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultHttpClientCodecMaxChunkSize;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultHttpClientCodecMaxHeaderSize;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultHttpClientCodecMaxInitialLineLength;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultIoThreadsCount;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultKeepAlive;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultKeepEncodingHeader;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultMaxConnections;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultMaxConnectionsPerHost;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultMaxRedirects;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultMaxRequestRetry;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultPooledConnectionIdleTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultReadTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultRequestTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultShutdownQuietPeriod;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultShutdownTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultSoKeepAlive;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultSoLinger;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultSoRcvBuf;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultSoReuseAddress;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultSoSndBuf;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultSslSessionCacheSize;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultSslSessionTimeout;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultStrict302Handling;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultTcpNoDelay;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultThreadPoolName;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUseInsecureTrustManager;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUseLaxCookieEncoder;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUseNativeTransport;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUseOnlyEpollNativeTransport;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUseOpenSsl;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUseProxyProperties;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUseProxySelector;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultUserAgent;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultValidateResponseHeaders;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultWebSocketMaxBufferSize;
+import static org.asynchttpclient.config.AsyncHttpClientConfigDefaults.defaultWebSocketMaxFrameSize;
 
 /**
  * Configuration class to use with a {@link AsyncHttpClient}. System property can be also used to configure this object default behavior by doing: <br>
@@ -62,7 +119,7 @@ public class DefaultAsyncHttpClientConfig implements AsyncHttpClientConfig {
 
     private final boolean enableAutomaticDecompression;
     private final String userAgent;
-    private final Realm realm;
+    private final @Nullable Realm realm;
     private final int maxRequestRetry;
     private final boolean disableUrlEncodingForBoundRequests;
     private final boolean useLaxCookieEncoder;
@@ -92,8 +149,8 @@ public class DefaultAsyncHttpClientConfig implements AsyncHttpClientConfig {
     private final int maxConnections;
     private final int maxConnectionsPerHost;
     private final int acquireFreeChannelTimeout;
-    private final ChannelPool channelPool;
-    private final ConnectionSemaphoreFactory connectionSemaphoreFactory;
+    private final @Nullable ChannelPool channelPool;
+    private final @Nullable ConnectionSemaphoreFactory connectionSemaphoreFactory;
     private final KeepAliveStrategy keepAliveStrategy;
 
     // ssl
@@ -101,13 +158,13 @@ public class DefaultAsyncHttpClientConfig implements AsyncHttpClientConfig {
     private final boolean useInsecureTrustManager;
     private final boolean disableHttpsEndpointIdentificationAlgorithm;
     private final int handshakeTimeout;
-    private final String[] enabledProtocols;
-    private final String[] enabledCipherSuites;
+    private final @Nullable String[] enabledProtocols;
+    private final @Nullable String[] enabledCipherSuites;
     private final boolean filterInsecureCipherSuites;
     private final int sslSessionCacheSize;
     private final int sslSessionTimeout;
-    private final SslContext sslContext;
-    private final SslEngineFactory sslEngineFactory;
+    private final @Nullable SslContext sslContext;
+    private final @Nullable SslEngineFactory sslEngineFactory;
 
     // filters
     private final List<RequestFilter> requestFilters;
@@ -126,20 +183,20 @@ public class DefaultAsyncHttpClientConfig implements AsyncHttpClientConfig {
     private final int httpClientCodecInitialBufferSize;
     private final int chunkedFileChunkSize;
     private final Map<ChannelOption<Object>, Object> channelOptions;
-    private final EventLoopGroup eventLoopGroup;
+    private final @Nullable EventLoopGroup eventLoopGroup;
     private final boolean useNativeTransport;
     private final boolean useOnlyEpollNativeTransport;
-    private final ByteBufAllocator allocator;
+    private final @Nullable ByteBufAllocator allocator;
     private final boolean tcpNoDelay;
     private final boolean soReuseAddress;
     private final boolean soKeepAlive;
     private final int soLinger;
     private final int soSndBuf;
     private final int soRcvBuf;
-    private final Timer nettyTimer;
-    private final ThreadFactory threadFactory;
-    private final Consumer<Channel> httpAdditionalChannelInitializer;
-    private final Consumer<Channel> wsAdditionalChannelInitializer;
+    private final @Nullable Timer nettyTimer;
+    private final @Nullable ThreadFactory threadFactory;
+    private final @Nullable Consumer<Channel> httpAdditionalChannelInitializer;
+    private final @Nullable Consumer<Channel> wsAdditionalChannelInitializer;
     private final ResponseBodyPartFactory responseBodyPartFactory;
     private final int ioThreadsCount;
     private final long hashedWheelTimerTickDuration;
@@ -152,7 +209,7 @@ private DefaultAsyncHttpClientConfig(// http
                                          boolean compressionEnforced,
                                          boolean enableAutomaticDecompression,
                                          String userAgent,
-                                         Realm realm,
+                                         @Nullable Realm realm,
                                          int maxRequestRetry,
                                          boolean disableUrlEncodingForBoundRequests,
                                          boolean useLaxCookieEncoder,
@@ -178,8 +235,8 @@ private DefaultAsyncHttpClientConfig(// http
                                          int maxConnections,
                                          int maxConnectionsPerHost,
                                          int acquireFreeChannelTimeout,
-                                         ChannelPool channelPool,
-                                         ConnectionSemaphoreFactory connectionSemaphoreFactory,
+                                         @Nullable ChannelPool channelPool,
+                                         @Nullable ConnectionSemaphoreFactory connectionSemaphoreFactory,
                                          KeepAliveStrategy keepAliveStrategy,
 
                                          // ssl
@@ -187,13 +244,13 @@ private DefaultAsyncHttpClientConfig(// http
                                          boolean useInsecureTrustManager,
                                          boolean disableHttpsEndpointIdentificationAlgorithm,
                                          int handshakeTimeout,
-                                         String[] enabledProtocols,
-                                         String[] enabledCipherSuites,
+                                         @Nullable String[] enabledProtocols,
+                                         @Nullable String[] enabledCipherSuites,
                                          boolean filterInsecureCipherSuites,
                                          int sslSessionCacheSize,
                                          int sslSessionTimeout,
-                                         SslContext sslContext,
-                                         SslEngineFactory sslEngineFactory,
+                                         @Nullable SslContext sslContext,
+                                         @Nullable SslEngineFactory sslEngineFactory,
 
                                          // filters
                                          List<RequestFilter> requestFilters,
@@ -222,14 +279,14 @@ private DefaultAsyncHttpClientConfig(// http
                                          int webSocketMaxBufferSize,
                                          int webSocketMaxFrameSize,
                                          Map<ChannelOption<Object>, Object> channelOptions,
-                                         EventLoopGroup eventLoopGroup,
+                                         @Nullable EventLoopGroup eventLoopGroup,
                                          boolean useNativeTransport,
                                          boolean useOnlyEpollNativeTransport,
-                                         ByteBufAllocator allocator,
-                                         Timer nettyTimer,
-                                         ThreadFactory threadFactory,
-                                         Consumer<Channel> httpAdditionalChannelInitializer,
-                                         Consumer<Channel> wsAdditionalChannelInitializer,
+                                         @Nullable ByteBufAllocator allocator,
+                                         @Nullable Timer nettyTimer,
+                                         @Nullable ThreadFactory threadFactory,
+                                         @Nullable Consumer<Channel> httpAdditionalChannelInitializer,
+                                         @Nullable Consumer<Channel> wsAdditionalChannelInitializer,
                                          ResponseBodyPartFactory responseBodyPartFactory,
                                          int ioThreadsCount,
                                          long hashedWheelTimerTickDuration,
@@ -370,7 +427,7 @@ public String getUserAgent() {
     }
 
     @Override
-    public Realm getRealm() {
+    public @Nullable Realm getRealm() {
         return realm;
     }
 
@@ -488,12 +545,12 @@ public int getAcquireFreeChannelTimeout() {
     }
 
     @Override
-    public ChannelPool getChannelPool() {
+    public @Nullable ChannelPool getChannelPool() {
         return channelPool;
     }
 
     @Override
-    public ConnectionSemaphoreFactory getConnectionSemaphoreFactory() {
+    public @Nullable ConnectionSemaphoreFactory getConnectionSemaphoreFactory() {
         return connectionSemaphoreFactory;
     }
 
@@ -529,12 +586,12 @@ public int getHandshakeTimeout() {
     }
 
     @Override
-    public String[] getEnabledProtocols() {
+    public @Nullable String[] getEnabledProtocols() {
         return enabledProtocols;
     }
 
     @Override
-    public String[] getEnabledCipherSuites() {
+    public @Nullable String[] getEnabledCipherSuites() {
         return enabledCipherSuites;
     }
 
@@ -554,12 +611,12 @@ public int getSslSessionTimeout() {
     }
 
     @Override
-    public SslContext getSslContext() {
+    public @Nullable SslContext getSslContext() {
         return sslContext;
     }
 
     @Override
-    public SslEngineFactory getSslEngineFactory() {
+    public @Nullable SslEngineFactory getSslEngineFactory() {
         return sslEngineFactory;
     }
 
@@ -658,7 +715,7 @@ public Map<ChannelOption<Object>, Object> getChannelOptions() {
     }
 
     @Override
-    public EventLoopGroup getEventLoopGroup() {
+    public @Nullable EventLoopGroup getEventLoopGroup() {
         return eventLoopGroup;
     }
 
@@ -673,12 +730,12 @@ public boolean isUseOnlyEpollNativeTransport() {
     }
 
     @Override
-    public ByteBufAllocator getAllocator() {
+    public @Nullable ByteBufAllocator getAllocator() {
         return allocator;
     }
 
     @Override
-    public Timer getNettyTimer() {
+    public @Nullable Timer getNettyTimer() {
         return nettyTimer;
     }
 
@@ -693,17 +750,17 @@ public int getHashedWheelTimerSize() {
     }
 
     @Override
-    public ThreadFactory getThreadFactory() {
+    public @Nullable ThreadFactory getThreadFactory() {
         return threadFactory;
     }
 
     @Override
-    public Consumer<Channel> getHttpAdditionalChannelInitializer() {
+    public @Nullable Consumer<Channel> getHttpAdditionalChannelInitializer() {
         return httpAdditionalChannelInitializer;
     }
 
     @Override
-    public Consumer<Channel> getWsAdditionalChannelInitializer() {
+    public @Nullable Consumer<Channel> getWsAdditionalChannelInitializer() {
         return wsAdditionalChannelInitializer;
     }
 
@@ -733,13 +790,13 @@ public static class Builder {
         private boolean compressionEnforced = defaultCompressionEnforced();
         private boolean enableAutomaticDecompression = defaultEnableAutomaticDecompression();
         private String userAgent = defaultUserAgent();
-        private Realm realm;
+        private @Nullable Realm realm;
         private int maxRequestRetry = defaultMaxRequestRetry();
         private boolean disableUrlEncodingForBoundRequests = defaultDisableUrlEncodingForBoundRequests();
         private boolean useLaxCookieEncoder = defaultUseLaxCookieEncoder();
         private boolean disableZeroCopy = defaultDisableZeroCopy();
         private boolean keepEncodingHeader = defaultKeepEncodingHeader();
-        private ProxyServerSelector proxyServerSelector;
+        private @Nullable ProxyServerSelector proxyServerSelector;
         private boolean useProxySelector = defaultUseProxySelector();
         private boolean useProxyProperties = defaultUseProxyProperties();
         private boolean validateResponseHeaders = defaultValidateResponseHeaders();
@@ -765,8 +822,8 @@ public static class Builder {
         private int maxConnections = defaultMaxConnections();
         private int maxConnectionsPerHost = defaultMaxConnectionsPerHost();
         private int acquireFreeChannelTimeout = defaultAcquireFreeChannelTimeout();
-        private ChannelPool channelPool;
-        private ConnectionSemaphoreFactory connectionSemaphoreFactory;
+        private @Nullable ChannelPool channelPool;
+        private @Nullable ConnectionSemaphoreFactory connectionSemaphoreFactory;
         private KeepAliveStrategy keepAliveStrategy = new DefaultKeepAliveStrategy();
 
         // ssl
@@ -774,13 +831,13 @@ public static class Builder {
         private boolean useInsecureTrustManager = defaultUseInsecureTrustManager();
         private boolean disableHttpsEndpointIdentificationAlgorithm = defaultDisableHttpsEndpointIdentificationAlgorithm();
         private int handshakeTimeout = defaultHandshakeTimeout();
-        private String[] enabledProtocols = defaultEnabledProtocols();
-        private String[] enabledCipherSuites = defaultEnabledCipherSuites();
+        private @Nullable String[] enabledProtocols = defaultEnabledProtocols();
+        private @Nullable String[] enabledCipherSuites = defaultEnabledCipherSuites();
         private boolean filterInsecureCipherSuites = defaultFilterInsecureCipherSuites();
         private int sslSessionCacheSize = defaultSslSessionCacheSize();
         private int sslSessionTimeout = defaultSslSessionTimeout();
-        private SslContext sslContext;
-        private SslEngineFactory sslEngineFactory;
+        private @Nullable SslContext sslContext;
+        private @Nullable SslEngineFactory sslEngineFactory;
 
         // cookie store
         private CookieStore cookieStore = new ThreadSafeCookieStore();
@@ -803,13 +860,13 @@ public static class Builder {
         private int chunkedFileChunkSize = defaultChunkedFileChunkSize();
         private boolean useNativeTransport = defaultUseNativeTransport();
         private boolean useOnlyEpollNativeTransport = defaultUseOnlyEpollNativeTransport();
-        private ByteBufAllocator allocator;
+        private @Nullable ByteBufAllocator allocator;
         private final Map<ChannelOption<Object>, Object> channelOptions = new HashMap<>();
-        private EventLoopGroup eventLoopGroup;
-        private Timer nettyTimer;
-        private ThreadFactory threadFactory;
-        private Consumer<Channel> httpAdditionalChannelInitializer;
-        private Consumer<Channel> wsAdditionalChannelInitializer;
+        private @Nullable EventLoopGroup eventLoopGroup;
+        private @Nullable Timer nettyTimer;
+        private @Nullable ThreadFactory threadFactory;
+        private @Nullable Consumer<Channel> httpAdditionalChannelInitializer;
+        private @Nullable Consumer<Channel> wsAdditionalChannelInitializer;
         private ResponseBodyPartFactory responseBodyPartFactory = ResponseBodyPartFactory.EAGER;
         private int ioThreadsCount = defaultIoThreadsCount();
         private long hashedWheelTickDuration = defaultHashedWheelTimerTickDuration();
diff --git a/client/src/main/java/org/asynchttpclient/DefaultRequest.java b/client/src/main/java/org/asynchttpclient/DefaultRequest.java
index a885e67a9..4170c33e2 100644
--- a/client/src/main/java/org/asynchttpclient/DefaultRequest.java
+++ b/client/src/main/java/org/asynchttpclient/DefaultRequest.java
@@ -23,6 +23,7 @@
 import org.asynchttpclient.request.body.generator.BodyGenerator;
 import org.asynchttpclient.request.body.multipart.Part;
 import org.asynchttpclient.uri.Uri;
+import org.jetbrains.annotations.Nullable;
 
 import java.io.File;
 import java.io.InputStream;
@@ -39,58 +40,58 @@
 
 public class DefaultRequest implements Request {
 
-    public final ProxyServer proxyServer;
+    public final @Nullable ProxyServer proxyServer;
     private final String method;
     private final Uri uri;
-    private final InetAddress address;
-    private final InetAddress localAddress;
+    private final @Nullable InetAddress address;
+    private final @Nullable InetAddress localAddress;
     private final HttpHeaders headers;
     private final List<Cookie> cookies;
-    private final byte[] byteData;
-    private final List<byte[]> compositeByteData;
-    private final String stringData;
-    private final ByteBuffer byteBufferData;
-    private final InputStream streamData;
-    private final BodyGenerator bodyGenerator;
+    private final byte @Nullable [] byteData;
+    private final @Nullable List<byte[]> compositeByteData;
+    private final @Nullable String stringData;
+    private final @Nullable ByteBuffer byteBufferData;
+    private final @Nullable InputStream streamData;
+    private final @Nullable BodyGenerator bodyGenerator;
     private final List<Param> formParams;
     private final List<Part> bodyParts;
-    private final String virtualHost;
-    private final Realm realm;
-    private final File file;
-    private final Boolean followRedirect;
+    private final @Nullable String virtualHost;
+    private final @Nullable Realm realm;
+    private final @Nullable File file;
+    private final @Nullable Boolean followRedirect;
     private final Duration requestTimeout;
     private final Duration readTimeout;
     private final long rangeOffset;
-    private final Charset charset;
+    private final @Nullable Charset charset;
     private final ChannelPoolPartitioning channelPoolPartitioning;
     private final NameResolver<InetAddress> nameResolver;
 
     // lazily loaded
-    private List<Param> queryParams;
+    private @Nullable List<Param> queryParams;
 
     public DefaultRequest(String method,
                           Uri uri,
-                          InetAddress address,
-                          InetAddress localAddress,
+                          @Nullable InetAddress address,
+                          @Nullable InetAddress localAddress,
                           HttpHeaders headers,
                           List<Cookie> cookies,
-                          byte[] byteData,
-                          List<byte[]> compositeByteData,
-                          String stringData,
-                          ByteBuffer byteBufferData,
-                          InputStream streamData,
-                          BodyGenerator bodyGenerator,
+                          byte @Nullable [] byteData,
+                          @Nullable List<byte[]> compositeByteData,
+                          @Nullable String stringData,
+                          @Nullable ByteBuffer byteBufferData,
+                          @Nullable InputStream streamData,
+                          @Nullable BodyGenerator bodyGenerator,
                           List<Param> formParams,
                           List<Part> bodyParts,
-                          String virtualHost,
-                          ProxyServer proxyServer,
-                          Realm realm,
-                          File file,
-                          Boolean followRedirect,
-                          Duration requestTimeout,
-                          Duration readTimeout,
+                          @Nullable String virtualHost,
+                          @Nullable ProxyServer proxyServer,
+                          @Nullable Realm realm,
+                          @Nullable File file,
+                          @Nullable Boolean followRedirect,
+                          @Nullable Duration requestTimeout,
+                          @Nullable Duration readTimeout,
                           long rangeOffset,
-                          Charset charset,
+                          @Nullable Charset charset,
                           ChannelPoolPartitioning channelPoolPartitioning,
                           NameResolver<InetAddress> nameResolver) {
         this.method = method;
@@ -136,12 +137,12 @@ public Uri getUri() {
     }
 
     @Override
-    public InetAddress getAddress() {
+    public @Nullable InetAddress getAddress() {
         return address;
     }
 
     @Override
-    public InetAddress getLocalAddress() {
+    public @Nullable InetAddress getLocalAddress() {
         return localAddress;
     }
 
@@ -156,32 +157,32 @@ public List<Cookie> getCookies() {
     }
 
     @Override
-    public byte[] getByteData() {
+    public byte @Nullable [] getByteData() {
         return byteData;
     }
 
     @Override
-    public List<byte[]> getCompositeByteData() {
+    public @Nullable List<byte[]> getCompositeByteData() {
         return compositeByteData;
     }
 
     @Override
-    public String getStringData() {
+    public @Nullable String getStringData() {
         return stringData;
     }
 
     @Override
-    public ByteBuffer getByteBufferData() {
+    public @Nullable ByteBuffer getByteBufferData() {
         return byteBufferData;
     }
 
     @Override
-    public InputStream getStreamData() {
+    public @Nullable InputStream getStreamData() {
         return streamData;
     }
 
     @Override
-    public BodyGenerator getBodyGenerator() {
+    public @Nullable BodyGenerator getBodyGenerator() {
         return bodyGenerator;
     }
 
@@ -196,27 +197,27 @@ public List<Part> getBodyParts() {
     }
 
     @Override
-    public String getVirtualHost() {
+    public @Nullable String getVirtualHost() {
         return virtualHost;
     }
 
     @Override
-    public ProxyServer getProxyServer() {
+    public @Nullable ProxyServer getProxyServer() {
         return proxyServer;
     }
 
     @Override
-    public Realm getRealm() {
+    public @Nullable Realm getRealm() {
         return realm;
     }
 
     @Override
-    public File getFile() {
+    public @Nullable File getFile() {
         return file;
     }
 
     @Override
-    public Boolean getFollowRedirect() {
+    public @Nullable Boolean getFollowRedirect() {
         return followRedirect;
     }
 
@@ -236,7 +237,7 @@ public long getRangeOffset() {
     }
 
     @Override
-    public Charset getCharset() {
+    public @Nullable Charset getCharset() {
         return charset;
     }
 
diff --git a/client/src/main/java/org/asynchttpclient/Param.java b/client/src/main/java/org/asynchttpclient/Param.java
index 397d5b5fa..cbc35e196 100644
--- a/client/src/main/java/org/asynchttpclient/Param.java
+++ b/client/src/main/java/org/asynchttpclient/Param.java
@@ -15,6 +15,8 @@
  */
 package org.asynchttpclient;
 
+import org.jetbrains.annotations.Nullable;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
@@ -27,14 +29,14 @@
 public class Param {
 
     private final String name;
-    private final String value;
+    private final @Nullable String value;
 
-    public Param(String name, String value) {
+    public Param(String name, @Nullable String value) {
         this.name = name;
         this.value = value;
     }
 
-    public static List<Param> map2ParamList(Map<String, List<String>> map) {
+    public static @Nullable List<Param> map2ParamList(Map<String, List<String>> map) {
         if (map == null) {
             return null;
         }
@@ -53,7 +55,7 @@ public String getName() {
         return name;
     }
 
-    public String getValue() {
+    public @Nullable String getValue() {
         return value;
     }
 
diff --git a/client/src/main/java/org/asynchttpclient/Realm.java b/client/src/main/java/org/asynchttpclient/Realm.java
index 271590da8..2006bd8b8 100644
--- a/client/src/main/java/org/asynchttpclient/Realm.java
+++ b/client/src/main/java/org/asynchttpclient/Realm.java
@@ -20,6 +20,7 @@
 import org.asynchttpclient.util.AuthenticatorUtils;
 import org.asynchttpclient.util.StringBuilderPool;
 import org.asynchttpclient.util.StringUtils;
+import org.jetbrains.annotations.Nullable;
 
 import java.nio.charset.Charset;
 import java.security.MessageDigest;
@@ -45,51 +46,51 @@ public class Realm {
     // MD5("")
     private static final String EMPTY_ENTITY_MD5 = "d41d8cd98f00b204e9800998ecf8427e";
 
-    private final String principal;
-    private final String password;
+    private final @Nullable String principal;
+    private final @Nullable String password;
     private final AuthScheme scheme;
-    private final String realmName;
-    private final String nonce;
-    private final String algorithm;
-    private final String response;
-    private final String opaque;
-    private final String qop;
+    private final @Nullable String realmName;
+    private final @Nullable String nonce;
+    private final @Nullable String algorithm;
+    private final @Nullable String response;
+    private final @Nullable String opaque;
+    private final @Nullable String qop;
     private final String nc;
-    private final String cnonce;
-    private final Uri uri;
+    private final @Nullable String cnonce;
+    private final @Nullable Uri uri;
     private final boolean usePreemptiveAuth;
     private final Charset charset;
     private final String ntlmHost;
     private final String ntlmDomain;
     private final boolean useAbsoluteURI;
     private final boolean omitQuery;
-    private final Map<String, String> customLoginConfig;
-    private final String servicePrincipalName;
+    private final @Nullable Map<String, String> customLoginConfig;
+    private final @Nullable String servicePrincipalName;
     private final boolean useCanonicalHostname;
-    private final String loginContextName;
-
-    private Realm(AuthScheme scheme,
-                  String principal,
-                  String password,
-                  String realmName,
-                  String nonce,
-                  String algorithm,
-                  String response,
-                  String opaque,
-                  String qop,
+    private final @Nullable String loginContextName;
+
+    private Realm(@Nullable AuthScheme scheme,
+                  @Nullable String principal,
+                  @Nullable String password,
+                  @Nullable String realmName,
+                  @Nullable String nonce,
+                  @Nullable String algorithm,
+                  @Nullable String response,
+                  @Nullable String opaque,
+                  @Nullable String qop,
                   String nc,
-                  String cnonce,
-                  Uri uri,
+                  @Nullable String cnonce,
+                  @Nullable Uri uri,
                   boolean usePreemptiveAuth,
                   Charset charset,
                   String ntlmDomain,
                   String ntlmHost,
                   boolean useAbsoluteURI,
                   boolean omitQuery,
-                  String servicePrincipalName,
+                  @Nullable String servicePrincipalName,
                   boolean useCanonicalHostname,
-                  Map<String, String> customLoginConfig,
-                  String loginContextName) {
+                  @Nullable Map<String, String> customLoginConfig,
+                  @Nullable String loginContextName) {
 
         this.scheme = assertNotNull(scheme, "scheme");
         this.principal = principal;
@@ -115,11 +116,11 @@ private Realm(AuthScheme scheme,
         this.loginContextName = loginContextName;
     }
 
-    public String getPrincipal() {
+    public @Nullable String getPrincipal() {
         return principal;
     }
 
-    public String getPassword() {
+    public @Nullable String getPassword() {
         return password;
     }
 
@@ -127,27 +128,27 @@ public AuthScheme getScheme() {
         return scheme;
     }
 
-    public String getRealmName() {
+    public @Nullable String getRealmName() {
         return realmName;
     }
 
-    public String getNonce() {
+    public @Nullable String getNonce() {
         return nonce;
     }
 
-    public String getAlgorithm() {
+    public @Nullable String getAlgorithm() {
         return algorithm;
     }
 
-    public String getResponse() {
+    public @Nullable String getResponse() {
         return response;
     }
 
-    public String getOpaque() {
+    public @Nullable String getOpaque() {
         return opaque;
     }
 
-    public String getQop() {
+    public @Nullable String getQop() {
         return qop;
     }
 
@@ -155,11 +156,11 @@ public String getNc() {
         return nc;
     }
 
-    public String getCnonce() {
+    public @Nullable String getCnonce() {
         return cnonce;
     }
 
-    public Uri getUri() {
+    public @Nullable Uri getUri() {
         return uri;
     }
 
@@ -202,11 +203,11 @@ public boolean isOmitQuery() {
         return omitQuery;
     }
 
-    public Map<String, String> getCustomLoginConfig() {
+    public @Nullable Map<String, String> getCustomLoginConfig() {
         return customLoginConfig;
     }
 
-    public String getServicePrincipalName() {
+    public @Nullable String getServicePrincipalName() {
         return servicePrincipalName;
     }
 
@@ -214,7 +215,7 @@ public boolean isUseCanonicalHostname() {
         return useCanonicalHostname;
     }
 
-    public String getLoginContextName() {
+    public @Nullable String getLoginContextName() {
         return loginContextName;
     }
 
@@ -255,18 +256,18 @@ public enum AuthScheme {
      */
     public static class Builder {
 
-        private final String principal;
-        private final String password;
-        private AuthScheme scheme;
-        private String realmName;
-        private String nonce;
-        private String algorithm;
-        private String response;
-        private String opaque;
-        private String qop;
+        private final @Nullable String principal;
+        private final @Nullable String password;
+        private @Nullable AuthScheme scheme;
+        private @Nullable String realmName;
+        private @Nullable String nonce;
+        private @Nullable String algorithm;
+        private @Nullable String response;
+        private @Nullable String opaque;
+        private @Nullable String qop;
         private String nc = DEFAULT_NC;
-        private String cnonce;
-        private Uri uri;
+        private @Nullable String cnonce;
+        private @Nullable Uri uri;
         private String methodName = GET;
         private boolean usePreemptive;
         private String ntlmDomain = System.getProperty("http.auth.ntlm.domain");
@@ -277,17 +278,17 @@ public static class Builder {
         /**
          * Kerberos/Spnego properties
          */
-        private Map<String, String> customLoginConfig;
-        private String servicePrincipalName;
+        private @Nullable Map<String, String> customLoginConfig;
+        private @Nullable String servicePrincipalName;
         private boolean useCanonicalHostname;
-        private String loginContextName;
+        private @Nullable String loginContextName;
 
         public Builder() {
             principal = null;
             password = null;
         }
 
-        public Builder(String principal, String password) {
+        public Builder(@Nullable String principal, @Nullable String password) {
             this.principal = principal;
             this.password = password;
         }
@@ -307,17 +308,17 @@ public Builder setScheme(AuthScheme scheme) {
             return this;
         }
 
-        public Builder setRealmName(String realmName) {
+        public Builder setRealmName(@Nullable String realmName) {
             this.realmName = realmName;
             return this;
         }
 
-        public Builder setNonce(String nonce) {
+        public Builder setNonce(@Nullable String nonce) {
             this.nonce = nonce;
             return this;
         }
 
-        public Builder setAlgorithm(String algorithm) {
+        public Builder setAlgorithm(@Nullable String algorithm) {
             this.algorithm = algorithm;
             return this;
         }
@@ -327,12 +328,12 @@ public Builder setResponse(String response) {
             return this;
         }
 
-        public Builder setOpaque(String opaque) {
+        public Builder setOpaque(@Nullable String opaque) {
             this.opaque = opaque;
             return this;
         }
 
-        public Builder setQop(String qop) {
+        public Builder setQop(@Nullable String qop) {
             if (isNonEmpty(qop)) {
                 this.qop = qop;
             }
@@ -344,7 +345,7 @@ public Builder setNc(String nc) {
             return this;
         }
 
-        public Builder setUri(Uri uri) {
+        public Builder setUri(@Nullable Uri uri) {
             this.uri = uri;
             return this;
         }
@@ -374,12 +375,12 @@ public Builder setCharset(Charset charset) {
             return this;
         }
 
-        public Builder setCustomLoginConfig(Map<String, String> customLoginConfig) {
+        public Builder setCustomLoginConfig(@Nullable Map<String, String> customLoginConfig) {
             this.customLoginConfig = customLoginConfig;
             return this;
         }
 
-        public Builder setServicePrincipalName(String servicePrincipalName) {
+        public Builder setServicePrincipalName(@Nullable String servicePrincipalName) {
             this.servicePrincipalName = servicePrincipalName;
             return this;
         }
@@ -389,12 +390,12 @@ public Builder setUseCanonicalHostname(boolean useCanonicalHostname) {
             return this;
         }
 
-        public Builder setLoginContextName(String loginContextName) {
+        public Builder setLoginContextName(@Nullable String loginContextName) {
             this.loginContextName = loginContextName;
             return this;
         }
 
-        private static String parseRawQop(String rawQop) {
+        private static @Nullable String parseRawQop(String rawQop) {
             String[] rawServerSupportedQops = rawQop.split(",");
             String[] serverSupportedQops = new String[rawServerSupportedQops.length];
             for (int i = 0; i < rawServerSupportedQops.length; i++) {
@@ -461,7 +462,7 @@ private void newCnonce(MessageDigest md) {
         /**
          * TODO: A Pattern/Matcher may be better.
          */
-        private static String match(String headerLine, String token) {
+        private static @Nullable String match(String headerLine, String token) {
             if (headerLine == null) {
                 return null;
             }
diff --git a/client/src/main/java/org/asynchttpclient/Request.java b/client/src/main/java/org/asynchttpclient/Request.java
index 42d53cb8e..0f8cdaa06 100644
--- a/client/src/main/java/org/asynchttpclient/Request.java
+++ b/client/src/main/java/org/asynchttpclient/Request.java
@@ -24,6 +24,7 @@
 import org.asynchttpclient.request.body.generator.BodyGenerator;
 import org.asynchttpclient.request.body.multipart.Part;
 import org.asynchttpclient.uri.Uri;
+import org.jetbrains.annotations.Nullable;
 
 import java.io.File;
 import java.io.InputStream;
@@ -65,12 +66,12 @@ public interface Request {
     /**
      * @return the InetAddress to be used to bypass uri's hostname resolution
      */
-    InetAddress getAddress();
+    @Nullable InetAddress getAddress();
 
     /**
      * @return the local address to bind from
      */
-    InetAddress getLocalAddress();
+    @Nullable InetAddress getLocalAddress();
 
     /**
      * @return the HTTP headers
@@ -85,32 +86,32 @@ public interface Request {
     /**
      * @return the request's body byte array (only non null if it was set this way)
      */
-    byte[] getByteData();
+    byte @Nullable [] getByteData();
 
     /**
      * @return the request's body array of byte arrays (only non null if it was set this way)
      */
-    List<byte[]> getCompositeByteData();
+    @Nullable List<byte[]> getCompositeByteData();
 
     /**
      * @return the request's body string (only non null if it was set this way)
      */
-    String getStringData();
+    @Nullable String getStringData();
 
     /**
      * @return the request's body ByteBuffer (only non null if it was set this way)
      */
-    ByteBuffer getByteBufferData();
+    @Nullable ByteBuffer getByteBufferData();
 
     /**
      * @return the request's body InputStream (only non null if it was set this way)
      */
-    InputStream getStreamData();
+    @Nullable InputStream getStreamData();
 
     /**
      * @return the request's body BodyGenerator (only non null if it was set this way)
      */
-    BodyGenerator getBodyGenerator();
+    @Nullable BodyGenerator getBodyGenerator();
 
     /**
      * @return the request's form parameters
@@ -125,7 +126,7 @@ public interface Request {
     /**
      * @return the virtual host to connect to
      */
-    String getVirtualHost();
+    @Nullable String getVirtualHost();
 
     /**
      * @return the query params resolved from the url/uri
@@ -135,22 +136,22 @@ public interface Request {
     /**
      * @return the proxy server to be used to perform this request (overrides the one defined in config)
      */
-    ProxyServer getProxyServer();
+    @Nullable ProxyServer getProxyServer();
 
     /**
      * @return the realm to be used to perform this request (overrides the one defined in config)
      */
-    Realm getRealm();
+    @Nullable Realm getRealm();
 
     /**
      * @return the file to be uploaded
      */
-    File getFile();
+    @Nullable File getFile();
 
     /**
      * @return if this request is to follow redirects. Non null values means "override config value".
      */
-    Boolean getFollowRedirect();
+    @Nullable Boolean getFollowRedirect();
 
     /**
      * @return the request timeout. Non zero values means "override config value".
@@ -170,7 +171,7 @@ public interface Request {
     /**
      * @return the charset value used when decoding the request's body.
      */
-    Charset getCharset();
+    @Nullable Charset getCharset();
 
     /**
      * @return the strategy to compute ChannelPool's keys
diff --git a/client/src/main/java/org/asynchttpclient/RequestBuilderBase.java b/client/src/main/java/org/asynchttpclient/RequestBuilderBase.java
index 059d9fe8b..0be0a8f44 100644
--- a/client/src/main/java/org/asynchttpclient/RequestBuilderBase.java
+++ b/client/src/main/java/org/asynchttpclient/RequestBuilderBase.java
@@ -26,7 +26,9 @@
 import org.asynchttpclient.request.body.generator.BodyGenerator;
 import org.asynchttpclient.request.body.multipart.Part;
 import org.asynchttpclient.uri.Uri;
+import org.asynchttpclient.util.EnsuresNonNull;
 import org.asynchttpclient.util.UriEncoder;
+import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -60,33 +62,33 @@ public abstract class RequestBuilderBase<T extends RequestBuilderBase<T>> {
     public static final NameResolver<InetAddress> DEFAULT_NAME_RESOLVER = new DefaultNameResolver(ImmediateEventExecutor.INSTANCE);
     // builder only fields
     protected UriEncoder uriEncoder;
-    protected List<Param> queryParams;
-    protected SignatureCalculator signatureCalculator;
+    protected @Nullable List<Param> queryParams;
+    protected @Nullable SignatureCalculator signatureCalculator;
 
     // request fields
     protected String method;
-    protected Uri uri;
-    protected InetAddress address;
-    protected InetAddress localAddress;
+    protected @Nullable Uri uri;
+    protected @Nullable InetAddress address;
+    protected @Nullable InetAddress localAddress;
     protected HttpHeaders headers;
-    protected ArrayList<Cookie> cookies;
-    protected byte[] byteData;
-    protected List<byte[]> compositeByteData;
-    protected String stringData;
-    protected ByteBuffer byteBufferData;
-    protected InputStream streamData;
-    protected BodyGenerator bodyGenerator;
-    protected List<Param> formParams;
-    protected List<Part> bodyParts;
-    protected String virtualHost;
-    protected ProxyServer proxyServer;
-    protected Realm realm;
-    protected File file;
-    protected Boolean followRedirect;
-    protected Duration requestTimeout;
-    protected Duration readTimeout;
+    protected @Nullable ArrayList<Cookie> cookies;
+    protected byte @Nullable [] byteData;
+    protected @Nullable List<byte[]> compositeByteData;
+    protected @Nullable String stringData;
+    protected @Nullable ByteBuffer byteBufferData;
+    protected @Nullable InputStream streamData;
+    protected @Nullable BodyGenerator bodyGenerator;
+    protected @Nullable List<Param> formParams;
+    protected @Nullable List<Part> bodyParts;
+    protected @Nullable String virtualHost;
+    protected @Nullable ProxyServer proxyServer;
+    protected @Nullable Realm realm;
+    protected @Nullable File file;
+    protected @Nullable Boolean followRedirect;
+    protected @Nullable Duration requestTimeout;
+    protected @Nullable Duration readTimeout;
     protected long rangeOffset;
-    protected Charset charset;
+    protected @Nullable Charset charset;
     protected ChannelPoolPartitioning channelPoolPartitioning = ChannelPoolPartitioning.PerHostChannelPoolPartitioning.INSTANCE;
     protected NameResolver<InetAddress> nameResolver = DEFAULT_NAME_RESOLVER;
 
@@ -293,6 +295,7 @@ public T setSingleHeaders(Map<? extends CharSequence, ?> headers) {
         return asDerivedType();
     }
 
+    @EnsuresNonNull("cookies")
     private void lazyInitCookies() {
         if (cookies == null) {
             cookies = new ArrayList<>(3);
@@ -413,6 +416,7 @@ public T setBody(BodyGenerator bodyGenerator) {
         return asDerivedType();
     }
 
+    @EnsuresNonNull("queryParams")
     public T addQueryParam(String name, String value) {
         if (queryParams == null) {
             queryParams = new ArrayList<>(1);
@@ -421,6 +425,7 @@ public T addQueryParam(String name, String value) {
         return asDerivedType();
     }
 
+    @EnsuresNonNull("queryParams")
     public T addQueryParams(List<Param> params) {
         if (queryParams == null) {
             queryParams = params;
@@ -434,7 +439,7 @@ public T setQueryParams(Map<String, List<String>> map) {
         return setQueryParams(Param.map2ParamList(map));
     }
 
-    public T setQueryParams(List<Param> params) {
+    public T setQueryParams(@Nullable List<Param> params) {
         // reset existing query
         if (uri != null && isNonEmpty(uri.getQuery())) {
             uri = uri.withNewQuery(null);
@@ -443,6 +448,7 @@ public T setQueryParams(List<Param> params) {
         return asDerivedType();
     }
 
+    @EnsuresNonNull("formParams")
     public T addFormParam(String name, String value) {
         resetNonMultipartData();
         resetMultipartData();
@@ -457,13 +463,14 @@ public T setFormParams(Map<String, List<String>> map) {
         return setFormParams(Param.map2ParamList(map));
     }
 
-    public T setFormParams(List<Param> params) {
+    public T setFormParams(@Nullable List<Param> params) {
         resetNonMultipartData();
         resetMultipartData();
         formParams = params;
         return asDerivedType();
     }
 
+    @EnsuresNonNull("bodyParts")
     public T addBodyPart(Part bodyPart) {
         resetFormParams();
         resetNonMultipartData();
@@ -474,6 +481,7 @@ public T addBodyPart(Part bodyPart) {
         return asDerivedType();
     }
 
+    @EnsuresNonNull("bodyParts")
     public T setBodyParts(List<Part> bodyParts) {
         this.bodyParts = new ArrayList<>(bodyParts);
         return asDerivedType();
@@ -539,7 +547,7 @@ public T setNameResolver(NameResolver<InetAddress> nameResolver) {
         return asDerivedType();
     }
 
-    public T setSignatureCalculator(SignatureCalculator signatureCalculator) {
+    public T setSignatureCalculator(@Nullable SignatureCalculator signatureCalculator) {
         this.signatureCalculator = signatureCalculator;
         return asDerivedType();
     }
@@ -595,6 +603,7 @@ private RequestBuilderBase<?> executeSignatureCalculator() {
         return rb;
     }
 
+    @EnsuresNonNull("charset")
     private void updateCharset() {
         String contentTypeHeader = headers.get(CONTENT_TYPE);
         Charset contentTypeCharset = extractContentTypeCharsetAttribute(contentTypeHeader);
diff --git a/client/src/main/java/org/asynchttpclient/Response.java b/client/src/main/java/org/asynchttpclient/Response.java
index 78a257e9c..8b9c9a6f1 100644
--- a/client/src/main/java/org/asynchttpclient/Response.java
+++ b/client/src/main/java/org/asynchttpclient/Response.java
@@ -20,6 +20,7 @@
 import io.netty.handler.codec.http.cookie.Cookie;
 import org.asynchttpclient.netty.NettyResponse;
 import org.asynchttpclient.uri.Uri;
+import org.jetbrains.annotations.Nullable;
 
 import java.io.InputStream;
 import java.net.SocketAddress;
@@ -176,8 +177,8 @@ public interface Response {
 
     class ResponseBuilder {
         private final List<HttpResponseBodyPart> bodyParts = new ArrayList<>(1);
-        private HttpResponseStatus status;
-        private HttpHeaders headers;
+        private @Nullable HttpResponseStatus status;
+        private @Nullable HttpHeaders headers;
 
         public void accumulate(HttpResponseStatus status) {
             this.status = status;
@@ -201,7 +202,7 @@ public void accumulate(HttpResponseBodyPart bodyPart) {
          *
          * @return a {@link Response} instance
          */
-        public Response build() {
+        public @Nullable Response build() {
             return status == null ? null : new NettyResponse(status, headers, bodyParts);
         }
 
diff --git a/client/src/main/java/org/asynchttpclient/oauth/OAuthSignatureCalculatorInstance.java b/client/src/main/java/org/asynchttpclient/oauth/OAuthSignatureCalculatorInstance.java
index 9363917a2..54401091f 100644
--- a/client/src/main/java/org/asynchttpclient/oauth/OAuthSignatureCalculatorInstance.java
+++ b/client/src/main/java/org/asynchttpclient/oauth/OAuthSignatureCalculatorInstance.java
@@ -21,6 +21,7 @@
 import org.asynchttpclient.util.StringBuilderPool;
 import org.asynchttpclient.util.StringUtils;
 import org.asynchttpclient.util.Utf8UrlEncoder;
+import org.jetbrains.annotations.Nullable;
 
 import javax.crypto.Mac;
 import javax.crypto.spec.SecretKeySpec;
@@ -155,7 +156,7 @@ private String encodedParams(ConsumerKey consumerAuth, RequestToken userAuth, lo
         return parameters.sortAndConcat();
     }
 
-    private static String percentEncodeAlreadyFormUrlEncoded(String s) {
+    private static String percentEncodeAlreadyFormUrlEncoded(@Nullable String s) {
         if (s == null) {
             return "";
         }
diff --git a/client/src/main/java/org/asynchttpclient/util/EnsuresNonNull.java b/client/src/main/java/org/asynchttpclient/util/EnsuresNonNull.java
new file mode 100644
index 000000000..a0cecaf8e
--- /dev/null
+++ b/client/src/main/java/org/asynchttpclient/util/EnsuresNonNull.java
@@ -0,0 +1,17 @@
+package org.asynchttpclient.util;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * NullAway supports @EnsuresNonNull(param) annotation, but org.jetbrains.annotations doesn't include this annotation.
+ * The purpose of this annotation is to tell NullAway that if the annotated method succeeded without any exceptions,
+ * all class's fields defined in "param" will be @NotNull.
+ */
+@Retention(RetentionPolicy.CLASS)
+@Target({ElementType.METHOD})
+public @interface EnsuresNonNull {
+    String[] value();
+}
diff --git a/pom.xml b/pom.xml
index 0e6809729..d5ee16304 100644
--- a/pom.xml
+++ b/pom.xml
@@ -63,6 +63,7 @@
         <slf4j.version>2.0.5</slf4j.version>
         <activation.version>2.0.1</activation.version>
         <logback.version>1.4.5</logback.version>
+        <jetbrains-annotations.version>24.0.1</jetbrains-annotations.version>
     </properties>
 
     <scm>
@@ -203,7 +204,7 @@
         <dependency>
             <groupId>org.jetbrains</groupId>
             <artifactId>annotations</artifactId>
-            <version>24.0.1</version>
+            <version>${jetbrains-annotations.version}</version>
         </dependency>
     </dependencies>
 
@@ -231,7 +232,8 @@
                             -Xep:NullablePrimitive:ERROR
                             -Xep:NullOptional:ERROR
                             -XepExcludedPaths:.*/src/test/java/.*
-                            -XepOpt:NullAway:AnnotatedPackages=org.asynchttpclient.channel,org.asynchttpclient.config,org.asynchttpclient.cookie,org.asynchttpclient.exception,org.asynchttpclient.filter,org.asynchttpclient.oauth,org.asynchttpclient.proxy,org.asynchttpclient.resolver
+                            -XepOpt:NullAway:AnnotatedPackages=org.asynchttpclient
+                            -XepOpt:NullAway:UnannotatedSubPackages=org.asynchttpclient.handler,org.asynchttpclient.netty,org.asynchttpclient.ntlm,org.asynchttpclient.request,org.asynchttpclient.spnego,org.asynchttpclient.uri,org.asynchttpclient.util,org.asynchttpclient.webdav,org.asynchttpclient.ws
                             -XepOpt:NullAway:AcknowledgeRestrictiveAnnotations=true
                             -Xep:NullAway:ERROR
                         </arg>