[FLINK-40852][table] Return NULL from PARSE_JSON and TRY_PARSE_JSON for NULL allowDuplicateKeys - #29343

What is the purpose of the change

PARSE_JSON and TRY_PARSE_JSON accept any BOOLEAN expression as the second argument (allowDuplicateKeys), not only literals. The runtime functions declared it as a primitive boolean, so a NULL value failed with a NullPointerException during unboxing:

SELECT PARSE_JSON('{}', CAST(NULL AS BOOLEAN));
-- java.lang.NullPointerException: Cannot invoke "java.lang.Boolean.booleanValue()" because "null" is null

The same happens for a nullable BOOLEAN column that is NULL for a row. With this change both functions return NULL in that case. The output type strategies (nullableIfArgs / forceNullable) already allow a NULL result.

JIRA: https://issues.apache.org/jira/browse/FLINK-40852

Brief change log

• ParseJsonFunction and TryParseJsonFunction take @Nullable Boolean allowDuplicateKeys and return NULL if it is NULL.

Verifying this change

This change added tests and can be verified as follows:

• Added SQL cases to JsonFunctionsITCase for PARSE_JSON and TRY_PARSE_JSON with a NULL BOOLEAN column as allowDuplicateKeys, expecting NULL. Both failed with the NPE before the fix.

There are no Table API cases for this because parseJson(boolean) / tryParseJson(boolean) only accept a literal.

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: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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

• Yes (please specify the tool below)

Generated-by: Claude Opus 5.5

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