Error Response when no matching functions

Send response to indicate no matching functions are found for the topic

Author: prsh9

types/invoker.go

@@ -63,6 +63,13 @@ func (i *Invoker) InvokeWithContext(ctx context.Context, topicMap *TopicMap, top
 	}
 
 	matchedFunctions := topicMap.Match(topic)
+	if len(matchedFunctions) == 0 {
+		i.Responses <- InvokerResponse{
+			Context: ctx,
+			Error:   fmt.Errorf("no functions to invoke"),
+		}
+	}
+
 	for _, matchedFunction := range matchedFunctions {
 		log.Printf("Invoke function: %s", matchedFunction)