修复了websocket逻辑错误

infrastructure/consumers.py

@@ -16,7 +16,10 @@ class KnockConsumer(WebsocketConsumer):
 
 def knock_knock(username, message):
     ws = user_dict.get(username)
-    message = json.dumps({'message': message})
-    ws.send(message)
-    print(message)
-    return True
+    if ws:
+        message = json.dumps({'message': message})
+        ws.send(message)
+        print(message)
+        return True
+    else:
+        return False