code: def _first_fill_value_loc(self):
          
          if len(self) == 0 or self.sp_index.npoints == len(self):
              return -1
  
          indices = self.sp_index.to_int_index().indices
          if not len(indices) or indices[0] > 0:
              return 0
  
          diff = indices[1:] - indices[:-1]
          return np.searchsorted(diff, 2) + 1
docs: Get the location of the first missing value.
  
          Returns
          -------
          int