docs: def _concrete_acl_list(self, acl_docs):
          """Concretize a list of ACL documents.
  
          :param list acl_docs: A list of ACL documents. Should come from the API.
          :returns: A list of :py:class:`ACL` objects.
          :rtype: list
          """
          if not acl_docs:
              return []
  
          return list(filter(None, [self._concrete_acl(acl_doc=doc) for doc in acl_docs]))