Update 'src/pubsub/pubsub/pubsub_library_v4.py'

src/pubsub/pubsub/pubsub_library_v4.py

@@ -116,6 +116,10 @@ class MinimalSubscriber(Node):
         self.msg = msg
         return
 
+    def has_msg(self):
+        # Check if a maessage has been received
+        return self.msg is not None
+
     def return_msg(self):
         return self.msg