Handle JSON response being None

[JLLeitschuh]

I just hit this strange case. Not sure what the server returned, but it certainly wasn't JSON. It may have been an empty response body.

However, "errors" not in result attempts to use result as an iterable, which fails when it is of type None with an unexpected error. This fix should make the error more intelligent.

  File "/Users/jonathanleitschuh/code/personal/security-research/moderne-campaign/venv/lib/python3.8/site-packages/gql/client.py", line 388, in execute
    data = loop.run_until_complete(
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
    return future.result()
  File "/Users/jonathanleitschuh/code/personal/security-research/moderne-campaign/venv/lib/python3.8/site-packages/gql/client.py", line 285, in execute_async
    return await session.execute(
  File "/Users/jonathanleitschuh/code/personal/security-research/moderne-campaign/venv/lib/python3.8/site-packages/gql/client.py", line 1220, in execute
    result = await self._execute(
  File "/Users/jonathanleitschuh/code/personal/security-research/moderne-campaign/venv/lib/python3.8/site-packages/gql/client.py", line 1126, in _execute
    result = await asyncio.wait_for(
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/asyncio/tasks.py", line 494, in wait_for
    return fut.result()
  File "/Users/jonathanleitschuh/code/personal/security-research/moderne-campaign/venv/lib/python3.8/site-packages/gql/transport/aiohttp.py", line 325, in execute
    if "errors" not in result and "data" not in result:
TypeError: argument of type 'NoneType' is not iterable

[codecov]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (0336607) compared to base (5e47f5f).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #365   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           24        24           
  Lines         2215      2217    +2     
=========================================
+ Hits          2215      2217    +2     

Impacted Files	Coverage Δ
gql/transport/aiohttp.py	100.00% <100.00%> (ø)

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[leszekhanusz]

Thanks for this PR and sorry for the delay.
Could you please fix the linting issue (running make check should do the trick) and also provide a test to fix the code coverage?

[JLLeitschuh]

What's the best way to test this? I'm just a user that encountered this issue, I don't have a huge amount of familiarity with testing python unfortunately.

[leszekhanusz]

I just hit this strange case. Not sure what the server returned, but it certainly wasn't JSON. It may have been an empty response body.

Yes, an empty json response triggers this bug.