bup ls error

mc@Debian-101-buster-64-minimal:~/backups$ bup ls
fatal: git show-ref: bad ref refs/heads/survival (8c03f9045d38524f25596ec5b75c54d1ff5ef22e)
Traceback (most recent call last):
  File "/usr/lib/bup/bup/main.py", line 317, in run_module_cmd
    import_and_run_main(module, args)
  File "/usr/lib/bup/bup/main.py", line 282, in import_and_run_main
    module.main(args)
  File "/usr/lib/bup/bup/cmd/ls.py", line 14, in main
    rc = ls.via_cmdline(argv[1:], out=out)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/bup/bup/ls.py", line 198, in via_cmdline
    return within_repo(repo, opt, out)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/bup/bup/ls.py", line 144, in within_repo
    for sub_name, sub_item in sorted(items, key=lambda x: x[0]):
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/bup/bup/vfs.py", line 927, in contents
    for x in item_gen:
  File "/usr/lib/bup/bup/vfs.py", line 604, in root_items
    for name, oid in tuple(repo.refs([], limit_to_heads=True)):
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/bup/bup/repo.py", line 78, in refs
    for ref in git.list_refs(patterns=patterns,
  File "/usr/lib/bup/bup/git.py", line 1048, in list_refs
    assert(not out)
           ^^^^^^^
AssertionError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/usr/lib/bup/bup/main.py", line 394, in <module>
    main()
  File "/usr/lib/bup/bup/main.py", line 391, in main
    wrap_main(lambda : run_subcmd(cmd_module, subcmd))
  File "/usr/lib/bup/bup/compat.py", line 82, in wrap_main
    sys.exit(main())
             ^^^^^^
  File "/usr/lib/bup/bup/main.py", line 391, in <lambda>
    wrap_main(lambda : run_subcmd(cmd_module, subcmd))
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/bup/bup/main.py", line 386, in run_subcmd
    run_module_cmd(module, args)
  File "/usr/lib/bup/bup/main.py", line 339, in run_module_cmd
    close_catpipes()
  File "/usr/lib/bup/bup/git.py", line 1406, in close_catpipes
    cp.close(wait=True)
  File "/usr/lib/bup/bup/git.py", line 1301, in close
    p.wait()
    ^^^^^^
AttributeError: 'NoneType' object has no attribute 'wait'