Error "AttributeError: 'NoneType' object has no attribute 'send'"

[Avarong]

When trying to use websockets.py for subscribing to idex data, ia have an error:
"
Traceback (most recent call last):
File "C:/Users/Administrator/PycharmProjects/untitled/IDEXbot.py", line 141, in
loop.run_until_complete(main())
File "C:\Users\Administrator\miniconda3\lib\asyncio\base_events.py", line 583, in run_until_complete
return future.result()
File "C:/Users/Administrator/PycharmProjects/untitled/IDEXbot.py", line 97, in main
await ism.subscribe(SubscribeCategory.markets,subscribe_list,['market_cancels', 'market_orders', 'market_trades'])
File "C:\Users\Administrator\PycharmProjects\untitled\idex\asyncio\websockets.py", line 246, in subscribe
await self._conn.send_message(category, req_msg)
File "C:\Users\Administrator\PycharmProjects\untitled\idex\asyncio\websockets.py", line 144, in send_message
await self._socket.send(socket_msg)
AttributeError: 'NoneType' object has no attribute 'send'
Unclosed client session
client_session: <aiohttp.client.ClientSession object at 0x000000E14FE061C8>
Unclosed connector
connections: ['[(<aiohttp.client_proto.ResponseHandler object at 0x000000E14FDF4358>, 355.937)]']
connector: <aiohttp.connector.TCPConnector object at 0x000000E14FE06208>
"
How should i fix that?