Fix bugs (GoogleCloudPlatform#203)

* Fix for when message is empty
* Updates IDE version for CI

Author: gguuss

.travis.yml

@@ -18,7 +18,7 @@ addons:
       - clang-format-5.0
 env:
   global:
-#    - ARDUINO_IDE_VERSION="1.8.10"
+     - ARDUINO_IDE_VERSION="1.8.13"
      - PRETTYNAME="Google Cloud IoT Arduino Library"
 # Optional, will default to "$TRAVIS_BUILD_DIR/Doxyfile"
 #    - DOXYFILE: $TRAVIS_BUILD_DIR/Doxyfile

examples/Esp8266-lwmqtt/esp8266_mqtt.h

@@ -29,12 +29,17 @@
 #include <CloudIoTCoreMqtt.h>
 #include "ciotc_config.h" // Wifi configuration here
 
+
 // !!REPLACEME!!
 // The MQTT callback function for commands and configuration updates
 // Place your message handler code here.
 void messageReceivedAdvanced(MQTTClient *client, char topic[], char bytes[], int length)
 {
-  Serial.printf("incoming: %s - %s\n", topic, length > 0 ? bytes : "[empty]");
+  if (length > 0){
+    Serial.printf("incoming: %s - %s\n", topic, bytes);
+  } else {
+    Serial.printf("0\n"); // Success but no message
+  }
 }
 ///////////////////////////////