Add pd.NaT to self

def _add_nat(self):
        """
        Add pd.NaT to self
        """
        if is_period_dtype(self):
            raise TypeError('Cannot add {cls} and {typ}'
                            .format(cls=type(self).__name__,
                                    typ=type(NaT).__name__))

        # GH#19124 pd.NaT is treated like a timedelta for both timedelta
        # and datetime dtypes
        result = np.zeros(len(self), dtype=np.int64)
        result.fill(iNaT)
        return type(self)(result, dtype=self.dtype, freq=None)