def isna(self) -> ArrayLike:
raise AbstractMethodError(self)<EOL>
A 1-D array indicating if each value is missing.

Returns
-------
na_values : Union[np.ndarray, ExtensionArray]
    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 :func:`ExtensionArray._reduce`
* ``na_values.any`` and ``na_values.all`` should be implemented