[jira] [Created] (CALCITE-4219) Clarify SqlCall#getOperandList() nullability

["Vladimir Sitnikov (Jira)" <ji...@apache.org>]

Vladimir Sitnikov created CALCITE-4219:
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             Summary: Clarify SqlCall#getOperandList() nullability
                 Key: CALCITE-4219
                 URL: https://issues.apache.org/jira/browse/CALCITE-4219
             Project: Calcite
          Issue Type: Sub-task
          Components: core
    Affects Versions: 1.25.0
            Reporter: Vladimir Sitnikov


{{getOperandList()}} is implemented by a number of different {{SqlCall}} sub-classes, and the list often includes null values.
The implementation is typically {{return ImmutableNullableList.of(...}}

However, {{getOperandList()}} is used a lot, and the code assumes that the resulting values are non-null. The same happens for {{SqlCall#operand(int)}}.

The workaround is to declare  {{getOperandList()}} and {{operand(int)}} to return non-nullable values (even though nulls are possible), and we could add suppressions at the side which returns {{ImmutableNullableList}}.

The solution might be behind the lines of adding {{nonNullableOperand(int)}}-like methods that would return non-nullable values and throw meaningful errors in case the value turns out to be null.

Another option might be to ensure all the fields are non-nullable (e.g. create dummy SqlNode for empty values).



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