parsing empty payload of stream message

[NoneGG]

I've come across similar problems occasionallyL

ERROR:asyncio:Task exception was never retrieved
--
  | future: <Task finished coro=<Subscriber.run() done, defined at /opt/app-root/src/lib/redis/async_subscriber.py:41> exception=TypeError("object of type 'NoneType' has no len()")>
  | Traceback (most recent call last):
  | File "/opt/app-root/src/lib/redis/async_subscriber.py", line 64, in run
  | last_id = await self.process_stream(last_id=last_id)
  | File "/opt/app-root/src/lib/redis/async_subscriber.py", line 160, in process_stream
  | **{self.stream_key: last_id},
  | File "/usr/local/lib/python3.7/site-packages/aredis/commands/streams.py", line 238, in xreadgroup
  | return await self.execute_command('XREADGROUP', *pieces)
  | File "/usr/local/lib/python3.7/site-packages/aredis/client.py", line 156, in execute_command
  | return await self.parse_response(connection, command_name, **options)
  | File "/usr/local/lib/python3.7/site-packages/aredis/client.py", line 174, in parse_response
  | return callback(response, **options)
  | File "/usr/local/lib/python3.7/site-packages/aredis/commands/streams.py", line 22, in multi_stream_list
  | result[r[0]] = stream_list(r[1])
  | File "/usr/local/lib/python3.7/site-packages/aredis/commands/streams.py", line 12, in stream_list
  | while len(kv_pairs) > 1:
  | TypeError: object of type 'NoneType' has no len()

It seems to happen when there's a "(nil)" payload for a given event:

127.0.0.1:6379> XREADGROUP GROUP group_name consumer_name STREAMS stream_name 0
1) 1) "stream_name"
   2) 1) 1) "1561724821836-0"
         2) (nil)
      2) 1) "1562178600447-0"
         2)  1) "stream"
             2) "stream_name"
             3) "topic"
             ...

This seems to happen when an XDEL occurs on a message, but that same message was never XACK. It'd be nice to return an empty dict() in those cases, so the client can clear it from the list but still process the other events pending.

Originally posted by @szelenka in #113 (comment)