QST: Zero copy access to the mask of a nullable array
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#### Question about pandas

Hello Pandas devs,
I was wondering what's the best zero-copy way to access the mask of a nullable array, say a StringArray for example. I noticed these all inherit from BaseMaskedArray which provides `isna()` wrapping `_mask` however I want to make sure this is the recommended method, if I can always be sure this doesn't incur a copy, etc. Should I be using `isna()` or something else, if it exists?


