[BEAM-1865]: Fix GroupByKeyInputVisitor for Direct Runner

[vikkyrk]

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• Also handle None input types which is the case when TypeOptions.pipeline_type_check is disabled.

[vikkyrk]

R: @aaltay @sb2nov

[coveralls]

Coverage increased (+0.003%) to 69.813% when pulling c7f1a44 on vikkyrk:py_gbk_type_check into 0c3dc00 on apache:master.

[asfbot]

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[coveralls]

Coverage increased (+0.003%) to 70.178% when pulling a0e5a07 on vikkyrk:py_gbk_type_check into 836e8e4 on apache:master.

[asfbot]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/beam_PreCommit_Java_MavenInstall/9369/
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[coveralls]

Coverage decreased (-0.003%) to 70.172% when pulling a0e5a07 on vikkyrk:py_gbk_type_check into 836e8e4 on apache:master.

[asfbot]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/beam_PreCommit_Java_MavenInstall/9370/
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