Fix null ref check in telemetry correlation Utils (#541)

* Fix null ref check in TelemetryCorrelationUtils

* Modifying log level to warning

* Updating Changelog

Author: dhaval24

CHANGELOG.md

@@ -1,5 +1,9 @@
 # CHANGELOG
 
+## Version 2.0.0
+
+- Fix #506 Null Reference Check causing Null Pointer Exception in `TelemetryCorrelationUtils.java`
+
 ## Version 2.0.0-BETA
 - Updating various dependencies to latest version
 - Introducing public class CustomClassWriter in Agent to enable finding common super classes used for Agent instrumentation without loading it

web/src/main/java/com/microsoft/applicationinsights/web/internal/correlation/TelemetryCorrelationUtils.java

@@ -111,7 +111,15 @@ public static void resolveCorrelation(HttpServletRequest request, HttpServletRes
 	public static String generateChildDependencyId() {
 
 		try {
+
 			RequestTelemetryContext context = ThreadContext.getRequestTelemetryContext();
+
+			//check if context is null - no correlation will happen
+			if (context == null) {
+				InternalLogger.INSTANCE.warn("No Correlation will happen, Thread context is null while generating child dependency");
+				return "";
+			}
+
 			RequestTelemetry requestTelemetry = context.getHttpRequestTelemetry();
 
 			String parentId = requestTelemetry.getContext().getOperation().getParentId();
@@ -137,6 +145,13 @@ public static String generateChildDependencyId() {
 	 * @return The correlation context as a string.
 	 */
 	public static String retrieveCorrelationContext() {
+
+		//check if context is null - no correlation will happen
+		if (ThreadContext.getRequestTelemetryContext() == null) {
+			InternalLogger.INSTANCE.warn("No correlation wil happen, Thread context is null");
+			return "";
+		}
+
 		CorrelationContext context = ThreadContext.getRequestTelemetryContext().getCorrelationContext();
 		return context.toString();
 	}
@@ -256,6 +271,13 @@ private static void resolveCorrelationContext(HttpServletRequest request, Reques
 			return;
 		}
 
+		//check if context is null - no correlation will happen
+		if (ThreadContext.getRequestTelemetryContext() == null) {
+			InternalLogger.INSTANCE.warn("No correlation will happen " +
+					"Thread context is null while resolving Correlation Context");
+			return;
+		}
+
 		CorrelationContext currentCorrelationContext = 
 			ThreadContext.getRequestTelemetryContext().getCorrelationContext();