docs: def empty(cls):
          """
          Returns an empty set. An empty set is unbounded and only contain the
          empty set.
  
              >>> intrange.empty() in intrange.empty()
              True
  
          It is unbounded but the boundaries are not infinite. Its boundaries are
          returned as ``None``. Every set contains the empty set.
          """
  
          self = cls.__new__(cls)
          self._range = _empty_internal_range
          return self