I'm facing this problem and I will be grateful if you can help me.

userID=self.serverProxy.addUser(data, ROOM_IDS.MAIN_ROOM,self,(host,port))
print("%s",userID)
buf= ctypes.create_string_buffer(8)
header=(typeMsg<<28)|(ack<<27)|(res<<26)|(ack_num<<13)|(self.seq_num)
struct.pack_into('>LHH', buf,0,header,8,userID)
self.transport.write(buf.raw)

The error is the following:

exceptions.TypeError: 'NoneType' object has no attribute '__getitem__'