RishavTiwari25 opened a new pull request, #26254:
URL: https://github.com/apache/datafusion/pull/26254
## Which issue does this PR close?
- Closes #26243.
## Rationale for this change
`array_concat([1, 2], NULL)` and `array_cat(NULL, [1, 2])` fail to plan with
`array_concat does not support type Int64`, even though the typed form
`array_concat([1, 2], NULL::int[])` works and PostgreSQL returns `{1,2}` for
`array_cat(ARRAY[1, 2], NULL)`.
`ArrayConcat::return_type` accepts `Null` arguments, but `coerce_types` ran
every argument through `coerced_type_with_base_type_only`, whose fallback turns
a non-list type into the base element type. The untyped `NULL` became `Int64`,
and the second `return_type` call rejected it.
## What changes are included in this PR?
`ArrayConcat::coerce_types` now coerces an untyped `NULL` argument to the
result list type, so the planner casts it to a `NULL` list and
`array_concat_inner` skips it like any other all-null argument. Other arguments
are coerced as before.
## What is the testing strategy for this PR?
New `sqllogictest` cases in `array/array_concat.slt` cover an untyped `NULL`
in the first, middle and last position, a nested list, the result type, and
`array_concat(NULL, NULL)`.
## Are there any user-facing changes?
`array_concat` / `array_cat` accept an untyped `NULL` argument instead of
failing to plan.
I used an AI coding assistant while working on this change; I have read the
diff and the tests and can walk through them.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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