docs: def from_name(cls, relation_name, conversations=None):
          """
          Find relation implementation in the current charm, based on the
          name of the relation.
  
          :return: A Relation instance, or None
          """
          if relation_name is None:
              return None
          relation_class = cls._cache.get(relation_name)
          if relation_class:
              return relation_class(relation_name, conversations)
          role, interface = hookenv.relation_to_role_and_interface(relation_name)
          if role and interface:
              relation_class = cls._find_impl(role, interface)
              if relation_class:
                  cls._cache[relation_name] = relation_class
                  return relation_class(relation_name, conversations)
          return None