[FLINK-18325] [table-common] Handle null when calling SqlDataTypeSpec#getNullable

[Aaaaaaron]

What is the purpose of the change

SqlDataTypeSpec#getNullable may return null(by Calcite design, it returns "Boolean" instead "boolean"), so the caller should handle null itself. In Calcite, every place calls this method adds the null judge.

Below is the code from Calcite.
org.apache.calcite.sql.SqlDataTypeSpec

  /** Whether data type allows nulls.
   *
   * <p>Nullable is nullable! Null means "not specified". E.g.
   * {@code CAST(x AS INTEGER)} preserves the same nullability as {@code x}.
   */
  private Boolean nullable;

Brief change log

Handle "null" when calling SqlDataTypeSpec#getNullable.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)

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Last check on commit 394a442 (Thu Oct 29 07:22:11 UTC 2020)

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[Aaaaaaron]

Can someone review this PR?

[wuchong]

From the implementation of ExtendedDataType in flink-sql-parser/parserImpls.ftl, the default nullable has been set to true. So it is always not null in Flink and it's safe to just call SqlDataTypeSpec#getNullable. However, I'm fine to add this null check. What do you think @danny0405 ?

[danny0405]

From the implementation of ExtendedDataType in flink-sql-parser/parserImpls.ftl, the default nullable has been set to true. So it is always not null in Flink and it's safe to just call SqlDataTypeSpec#getNullable. However, I'm fine to add this null check. What do you think @danny0405 ?

Yes, we always set the flag in Flink so it should be null-safe, but adding an explicit check is better(in case maybe there are some changes in the parser later on).

[wuchong]

Thanks @danny0405 . Then I'm fine with this PR.

LGTM.

[wuchong]

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