code: def _sub_nat(self):
          
          # GH#19124 Timedelta - datetime is not in general well-defined.
          # We make an exception for pd.NaT, which in this case quacks
          # like a timedelta.
          # For datetime64 dtypes by convention we treat NaT as a datetime, so
          # this subtraction returns a timedelta64 dtype.
          # For period dtype, timedelta64 is a close-enough return dtype.
          result = np.zeros(len(self), dtype=np.int64)
          result.fill(iNaT)
          return result.view('timedelta64[ns]')
docs: Subtract pd.NaT from self