[C++] Uniform null handling in compute functions

[asfimport]

The compute functions today have mixed support for null types.

Unary arithmetic functions (e.g. abs) don't support null arrays

Binary arithmetic functions (e.g. add) support one null array (e.g. int32 + null) but not both null arrays (i.e. null + null) but they do support both values being null (e.g. [null] + [null] = [null] if dtype=int32 but not supported if dtype=null)

sort_indices should support null arrays.

Some functions do forward null arrays:

• unique

  Some functions output a non-null type given null inputs

• is_null (=> boolean)

• is_valid (=> boolean)

• value_counts (=> struct)

• dictionary_encode (=> dictionary)

• count (=> int64)

  Some functions throw an error other than "not implemented"

• list_parent_indices

Reporter: Weston Pace / @westonpace
Assignee: David Li / @lidavidm

PRs and other links:

• GitHub Pull Request #11255

_{Note: This issue was originally created as ARROW-13876. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 11255
#11255