[C++][Python] Casting map causes pyarrow to crash

[rohanjain101]

Describe the bug, including details regarding any error messages, version, and platform.

>>> import pyarrow as pa
>>> z = pa.array([{1: 2}], type=pa.map_(pa.int64(), pa.int64()))
>>> z.cast(pa.map_(pa.int32(), pa.int64()))
arrow/cpp/src/arrow/array/array_nested.cc:431: Check failed: _s.ok() Operation failed: ValidateChildData(data->child_data)
Bad status: Invalid: Map array keys array should have no nulls

Component(s)

Python

[felipecrv]

The fix for this is the same as #41070. Change the MapArray validation code in array_nested.cc to use MayHaveNulls() instead of arr->null_count != 0.

[felipecrv]

Issue resolved by pull request 41957
#41957