[FLINK-40236][python] Fix _infer_type inferring ARRAY<NULL> for a list with a leading None

[nikolauspschuetz]

What is the purpose of the change

_infer_type in flink-python/pyflink/table/types.py inferred a list's element type from obj[0] instead of the first non-None element it scans for. When the first element is None, the array element type collapsed to NULL, making schema inference order-dependent:

_infer_type([1, None]) -> ArrayType(BigIntType)   # correct
_infer_type([None, 1]) -> ArrayType(NullType)     # wrong; should be BigIntType

The dict branch just above already handles this correctly (it infers from the found non-None value). from_elements([Row(c=[None, 1])]) without an explicit schema infers ARRAY<NULL>, which then typically errors downstream.

Brief change log

• Infer the array element type from the scanned non-None element v rather than obj[0].

Verifying this change

This change added a test and can be verified as follows:

• Added TypesTests.test_infer_array_type_with_leading_none asserting _infer_type([None, 1]) yields ArrayType(BigIntType).
• Verified against the released apache-flink wheel: the array element type is NullType before the fix and BigIntType after (the all-None case still yields ARRAY<NULL>).

The two commits demonstrate this: the first adds the test only (CI red — test_infer_array_type_with_leading_none fails with AssertionError: False is not true), the second applies the fix (CI green). Runs on my fork:

• test only (fails): https://github.com/nikolauspschuetz/flink/actions/runs/30144289029/job/89646257914
• with fix (passes): https://github.com/nikolauspschuetz/flink/actions/runs/30146231008/job/89649334451 (types module 457 passed / 2 skipped)

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no

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Was generative AI tooling used to co-author this PR?

• Yes (Claude Code)

Generated-by: Claude Code (Opus 4.8)

[flinkbot]

CI report:

• 1dc127f Azure: SUCCESS

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