add throwable only if not null

Author: nhulston

dd-java-agent/instrumentation/aws-lambda-handler/src/main/java/datadog/trace/instrumentation/aws/v1/lambda/LambdaHandlerInstrumentation.java

@@ -112,7 +112,9 @@ static void exit(
 
       try {
         final AgentSpan span = scope.span();
-        span.addThrowable(throwable);
+        if (throwable != null) {
+          span.addThrowable(throwable);
+        }
         span.finish();
         AgentTracer.get().notifyExtensionEnd(span, result, null != throwable);
       } finally {