code: def compress_repr(self) -> Optional[str]:
          
          string = super().compress_repr()
          if string is not None:
              return string
          results = []
          mask = self.mask
          refindices = mask.refindices.values
          for (key, value) in self.MODEL_CONSTANTS.items():
              if value in mask.RELEVANT_VALUES:
                  unique = numpy.unique(self.values[refindices == value])
                  unique = self.revert_timefactor(unique)
                  length = len(unique)
                  if length == 1:
                      results.append(
                          f'{key.lower()}={objecttools.repr_(unique[0])}')
                  elif length > 1:
                      return None
          return ', '.join(sorted(results))
docs: Works as |Parameter.compress_repr|, but alternatively
          tries to compress by following an external classification.
  
          See the main documentation on class |ZipParameter| for
          further information.