A 1-D array indicating if each value is missing.
In most cases, this should return a NumPy ndarray. For exceptional cases like SparseArray, where returning an ndarray would be expensive, an ExtensionArray may be returned.
Notes
If returning an ExtensionArray, then
na_values._is_boolean should be True
na_values should implement ExtensionArray._reduce()
na_values.any and na_values.all should be implemented
Examples
>>> arr = pd.array([1, 2, np.nan, np.nan])
>>> arr.isna()
array([False, False, True, True])
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https://pandas.pydata.org/pandas-docs/version/2.3.0/reference/api/pandas.api.extensions.ExtensionArray.isna.html