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

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]))