Fix cast to null
_The documentation is not available anymore as the PR was closed or merged._
It currently fails with `ArrowNotImplementedError` instead of `TypeError` when one tries to cast integer to null type.

Because if this, type inference breaks when one replaces null values with integers in `map` (it first tries to cast to the previous type before inferring the new type).

Fix https://github.com/huggingface/datasets/issues/4483