Descendants on multiple members

[cubewise-gng]

Unable to build the DESCENDANTS mdx expression against a set of multiple members.

hierarchy_set = MdxHierarchySet.descendants( MdxHierarchySet.members([Member.of('Dimension', 'Hierarchy', 'Member1'), Member.of('Dimension', 'Hierarchy', 'Member2')]).to_mdx()

getting error:
AttributeError: 'ElementsHierarchySet' object has no attribute 'unique_name'
mdxpy\mdx.py:869: AttributeError