fix: remove redundant message in streaming (#739)

Because

- There is a redundant `null` message at the end of streaming.

This commit

- Removes redundant message in streaming

pkg/handler/triggerhandler.go

@@ -281,6 +281,11 @@ func HandleTrigger(mux *runtime.ServeMux, client pb.PipelinePublicServiceClient,
 			return
 		}
 	}
+	// When using `streamHandler`, we should directly close the response once
+	// the event stream is completed to prevent redundant events.
+	if sh != nil {
+		return
+	}
 
 	annotatedContext = runtime.NewServerMetadataContext(annotatedContext, md)
 
@@ -594,6 +599,11 @@ func HandleTriggerRelease(mux *runtime.ServeMux, client pb.PipelinePublicService
 			return
 		}
 	}
+	// When using `streamHandler`, we should directly close the response once
+	// the event stream is completed to prevent redundant events.
+	if sh != nil {
+		return
+	}
 
 	annotatedContext = runtime.NewServerMetadataContext(annotatedContext, md)