Handle Nones in PyArrow struct
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2022-03-03T15:24:18Z
https://github.com/huggingface/datasets/pull/3814#issuecomment-1058152965
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2022-03-03T15:24:18Z
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This PR fixes an issue introduced by #3575 where `None` values stored in PyArrow arrays/structs would get ignored by `cast_storage` or by the `pa.array(cast_to_python_objects(..))` pattern. To fix the former, it also bumps the minimal PyArrow version to v5.0.0 to use the `mask` param in `pa.SturctArray`. 

