Does this package support union type fragments?

Start with gql/query_parser.py, especially parse and the selection-set handling shown in the traceback; inspect how gql run in gql/cli.py passes the document to the parser. Reproduce the supplied query, then verify that union type fragments parse without the IndexError.

I have a .graphql file that looks like this:

query GetBook($id: UUID!) {
  book(id: $id) {
    author {
      id
      name
      ... on FantasyAuthor {
        fantasyBooksWritten
      }
      ... on SciFiAuthor {
        sciFiBooksWritten
      }
    }
  }
}

However, when I run gql run I get the following error:

Parsing /home/user/python-test/book_query.graphql ... Traceback (most recent call last):
  File "/home/user/.local/bin/gql", line 11, in <module>
    sys.exit(cli())
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/home/user/.local/lib/python3.8/site-packages/gql/cli.py", line 99, in run
    process_file(filename, query_parser, query_renderer)
  File "/home/user/.local/lib/python3.8/site-packages/gql/cli.py", line 68, in process_file
    parsed = parser.parse(query)
  File "/home/user/.local/lib/python3.8/site-packages/gql/query_parser.py", line 243, in parse
    visit(document_ast, TypeInfoVisitor(type_info, visitor))
  File "/home/user/.local/lib/python3.8/site-packages/graphql/language/visitor.py", line 286, in visit
    result = visit_fn(visitor, node, key, parent, path, ancestors)
  File "/home/user/.local/lib/python3.8/site-packages/graphql/language/visitor.py", line 394, in leave
    result = fn(self.visitor, node, *args) if fn else None
  File "/home/user/.local/lib/python3.8/site-packages/gql/query_parser.py", line 109, in leave_selection_set
    self.pull()
  File "/home/user/.local/lib/python3.8/site-packages/gql/query_parser.py", line 70, in pull
    return self.dfs_path.pop()
IndexError: pop from empty list

wondering if anyone has seen similar issues. Thanks!