[BEAM-7530] allow read None bytes

[Juta]

bugfix when reading None values from bigquery

Traceback (most recent call last):
  File "/mnt/c/Users/Juta/Documents/02-projects/apache/beam/sdks/venv/lib/python3.5/site-packages/apache_beam/runners/direct/executor.py", line 343, in call
    finish_state)
  File "/mnt/c/Users/Juta/Documents/02-projects/apache/beam/sdks/venv/lib/python3.5/site-packages/apache_beam/runners/direct/executor.py", line 383, in attempt_call
    result = evaluator.finish_bundle()
  File "/mnt/c/Users/Juta/Documents/02-projects/apache/beam/sdks/venv/lib/python3.5/site-packages/apache_beam/runners/direct/transform_evaluator.py", line 319, in finish_bundle
    bundles = _read_values_to_bundles(reader)
  File "/mnt/c/Users/Juta/Documents/02-projects/apache/beam/sdks/venv/lib/python3.5/site-packages/apache_beam/runners/direct/transform_evaluator.py", line 306, in _read_values_to_bundles
    read_result = [GlobalWindows.windowed_value(e) for e in reader]
  File "/mnt/c/Users/Juta/Documents/02-projects/apache/beam/sdks/venv/lib/python3.5/site-packages/apache_beam/runners/direct/transform_evaluator.py", line 306, in <listcomp>
    read_result = [GlobalWindows.windowed_value(e) for e in reader]
  File "/mnt/c/Users/Juta/Documents/02-projects/apache/beam/sdks/venv/lib/python3.5/site-packages/apache_beam/io/gcp/bigquery_tools.py", line 932, in __iter__
    row.f[i].v.string_value = row.f[i].v.string_value.encode('utf-8')
AttributeError: 'NoneType' object has no attribute 'string_value'

Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

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[Juta]

Run Python PostCommit

[Juta]

R: @tvalentyn

[tvalentyn]

Thanks a lot! Could you please add to one of BQ IT tests a test scenario that reads and writes a row of None values for BQ datatypes that allow value to be None ?

Thank you!

[tvalentyn]

We can merge this to make sure that 2.14 picks up the fix, but please add the missing test scenarios in a follow-up change. Thank you.

[tvalentyn]

@pabloem could you please help with the merge?

[Juta]

Thanks @tvalentyn. I will add a test for this scenario next week

[tvalentyn]

ping @pabloem :-)

[tvalentyn]

@aaltay or @chamikaramj - Could you please help with the merge? Thanks!