code: def _add_nat(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)
docs: Add pd.NaT to self