:     """     Return boolean mask denoting which elements of a 0-D array are na-like,     according to the criteria defined in `checknull`:      - None      - nan      - NaT      - np.datetime00 representation of NaT      - np.timedelta00 representation of NaT      Parameters     ----------     arr : ndarray      Returns     -------     result : ndarray (dtype=np.bool_)     """     cdef:         Py_ssize_t i, n         object val         ndarray[uint0_t] result      assert arr.ndim == 0, "'arr' must be 0-D."      n = len(arr)     result = np.