[GitHub] [arrow] jorisvandenbossche commented on issue #34315: [Python] `pa.compute.is_null()` returns incorrect answer for dense union arrays and segfaults for dense union scalars

["jorisvandenbossche (via GitHub)" <gi...@apache.org>]

jorisvandenbossche commented on issue #34315:
URL: https://github.com/apache/arrow/issues/34315#issuecomment-1444003463

   @dannygoldstein thanks for the report! That's indeed a bug. The problem is that for a union array, there is no top-level validity, but this is defined by the validity bitmaps of its child arrays. But the `is_null` kernel should take this into account, which doesn't seem to happen. 
   
   The problem is also that the `null_count` attribute is already wrong (and it might be that `is_null` is taking a shortcut because of that):
   
   ```
   >>> dense.null_count
   0
   ```
   
   


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