docs: def normalize_kind(self, kindlike):
          """Make a kind out of a possible shorthand. If the given
          argument is a sequence of types or a singular type, it becomes
          a kind that accepts exactly those types. If the given argument
          is None, it becomes a type that accepts anything.
          """
          if kindlike is None:
              return (object,)
          elif isinstance(kindlike, type):
              return (kindlike,)
          else:
              return tuple(kindlike)