Vladimir Sitnikov created CALCITE-4222:
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Summary: Clarify if null elements are allowed in RelTraitSet
Key: CALCITE-4222
URL: https://issues.apache.org/jira/browse/CALCITE-4222
Project: Calcite
Issue Type: Sub-task
Components: core
Affects Versions: 1.25.0
Reporter: Vladimir Sitnikov
Currently, one-half of the methods in {{RelTraitSet}} fails with NPE, and
another half does have some null-checks. Then there are {{getDefault()}} and
{{isDefault()}}
AFAIK the only way to create a traitset with null element currently is to
implement {{org.apache.calcite.plan.RelTraitDef#getDefault}} to return {{null}}
(which never happens in Calcite code).
However, such a traitset would likely fail with NPE in
{{org.apache.calcite.plan.RelTraitSet#satisfies}} quite fast.
{{RelCollationTraitDef}} and {{RelDistributionTraitDef}} have non-null default
value which might interfere with collation and distribution metadata. For
instance, {{distribution}} metadata might return null, and then it would fail
with NPE when replacing distribution trait.
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