Fix MiscUtils: closeSilently should check for nullity, close AsyncHttpClient#662

Author: Stephane Landelle

api/src/main/java/org/asynchttpclient/util/MiscUtils.java

@@ -52,9 +52,10 @@ public static <T> T withDefault(T value, T defaults) {
     }
 
     public static void closeSilently(Closeable closeable) {
-        try {
-            closeable.close();
-        } catch (IOException e) {
-        }
+        if (closeable != null)
+            try {
+                closeable.close();
+            } catch (IOException e) {
+            }
     }
 }