"'NoneType' object is not callable" if lz4 compression enabled on server but lib not installed

[mstump]

The library errors with a cryptic message if lz4 compression is enabled on the Kafka cluster but the corresponding Python library is not installed on the consumer/broker. It took a while to diagnose so I wanted to advocate for a better error message. Worst case I wanted to log the stack trace so it's indexed by Google and resolvable by future users.

[2018-12-17 18:16:55,621: ERROR]: [^--Consumer]: Drain messages raised: TypeError("'NoneType' object is not callable")
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/faust/transport/consumer.py", line 501, in _drain_messages
    async for tp, message in ait:
  File "/usr/local/lib/python3.7/site-packages/faust/transport/drivers/aiokafka.py", line 322, in getmany
    timeout=timeout,
  File "/usr/local/lib/python3.7/site-packages/faust/transport/drivers/aiokafka.py", line 695, in getmany
    timeout=timeout,
  File "/usr/local/lib/python3.7/site-packages/mode/threads.py", line 339, in call_thread
    result = await promise
  File "/usr/local/lib/python3.7/site-packages/mode/threads.py", line 284, in _process_enqueued
    result = await maybe_async(method(*args, **kwargs))
  File "/usr/local/lib/python3.7/site-packages/mode/utils/futures.py", line 109, in maybe_async
    return await res
  File "/usr/local/lib/python3.7/site-packages/aiokafka/consumer/fetcher.py", line 867, in fetched_records
    records = res_or_error.getall(max_records)
  File "/usr/local/lib/python3.7/site-packages/aiokafka/consumer/fetcher.py", line 133, in getall
    for msg in next_batch_iter:
  File "/usr/local/lib/python3.7/site-packages/aiokafka/consumer/fetcher.py", line 985, in _unpack_records
    for record in next_batch:
  File "aiokafka/record/_legacy_records.pyx", line 238, in __iter__
  File "aiokafka/record/_legacy_records.pyx", line 136, in aiokafka.record._legacy_records._LegacyRecordBatchCython._decompress
TypeError: 'NoneType' object is not callable

[trnkatomas]

I particularly dislike this:

except ImportError:
    lz4 = None

I think it should be either logged at least as a DEBUG message if handled like this or If you don't solve at all, the error would be more obvious than generic None type error

[wc571498244]

Running this command can solve pip install lz4