hunger_cleanroom build fail

 FAIL  Generation of "system-moses" failed: join() argument must be str, bytes, or os.PathLike object, not 'NoneType'

Error report:
>>>>>> Flushing buffer:
 FAIL  Generation of "system-moses" failed: join() argument must be str, bytes, or os.PathLike object, not 'NoneType'

>>>>>> End of Buffer <<<<<<


Traceback Information:
  File "/home/paul/hunger_cleanroom/cleanroom/generator.py", line 101, in generate_systems
    exe.run(
  File "/home/paul/hunger_cleanroom/cleanroom/executor.py", line 61, in run
    command.execute_func(
  File "/home/paul/hunger_cleanroom/cleanroom/commandmanager.py", line 191, in <lambda>
    execute_func=lambda loc, sc, *args, **kwargs: __execute_func(
  File "/home/paul/hunger_cleanroom/cleanroom/commandmanager.py", line 177, in __execute_func
    call_command(location, system_context, cmd, *args, **kwargs)
  File "/home/paul/hunger_cleanroom/cleanroom/commandmanager.py", line 55, in call_command
    command(location, system_context, *_args, **_kwargs)
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 253, in __call__
    self.prepare_for_export(location, system_context)
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 311, in prepare_for_export
    ) = self._create_cache_data(location, system_context, has_kernel=has_kernel)
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 340, in _create_cache_data
    squashfs_file = self._create_squashfs(
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 467, in _create_squashfs
    squash_file = os.path.join(
  File "/usr/lib/python3.8/posixpath.py", line 90, in join
    genericpath._check_arg_types('join', a, *p)
  File "/usr/lib/python3.8/genericpath.py", line 152, in _check_arg_types
    raise TypeError(f'{funcname}() argument must be str, bytes, or '


>>>>>> END OF ERROR REPORT <<<<<<
Traceback (most recent call last):
  File "/home/paul/hunger_cleanroom/cleanroom/generator.py", line 101, in generate_systems
    exe.run(
  File "/home/paul/hunger_cleanroom/cleanroom/executor.py", line 61, in run
    command.execute_func(
  File "/home/paul/hunger_cleanroom/cleanroom/commandmanager.py", line 191, in <lambda>
    execute_func=lambda loc, sc, *args, **kwargs: __execute_func(
  File "/home/paul/hunger_cleanroom/cleanroom/commandmanager.py", line 177, in __execute_func
    call_command(location, system_context, cmd, *args, **kwargs)
  File "/home/paul/hunger_cleanroom/cleanroom/commandmanager.py", line 55, in call_command
    command(location, system_context, *_args, **_kwargs)
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 253, in __call__
    self.prepare_for_export(location, system_context)
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 311, in prepare_for_export
    ) = self._create_cache_data(location, system_context, has_kernel=has_kernel)
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 340, in _create_cache_data
    squashfs_file = self._create_squashfs(
  File "/home/paul/hunger_cleanroom/cleanroom/commands/export.py", line 467, in _create_squashfs
    squash_file = os.path.join(
  File "/usr/lib/python3.8/posixpath.py", line 90, in join
    genericpath._check_arg_types('join', a, *p)
  File "/usr/lib/python3.8/genericpath.py", line 152, in _check_arg_types
    raise TypeError(f'{funcname}() argument must be str, bytes, or '
TypeError: join() argument must be str, bytes, or os.PathLike object, not 'NoneType'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/paul/hunger_cleanroom/clrm", line 13, in <module>
    main.run()
  File "/home/paul/hunger_cleanroom/cleanroom/main.py", line 104, in run
    main(*sys.argv)
  File "/home/paul/hunger_cleanroom/cleanroom/main.py", line 183, in main
    generator.generate_systems(
  File "/home/paul/hunger_cleanroom/cleanroom/generator.py", line 108, in generate_systems
    self._report_error(system_name, e, ignore_errors=ignore_errors)
  File "/home/paul/hunger_cleanroom/cleanroom/generator.py", line 41, in _report_error
    self._report_error_details(system, exception, ignore_errors=ignore_errors)
  File "/home/paul/hunger_cleanroom/cleanroom/generator.py", line 61, in _report_error_details
    raise GenerateError("Generation failed.", original_exception=exception)
cleanroom.exceptions.GenerateError: Error: Generation failed.
    Trigger: join() argument must be str, bytes, or os.PathLike object, not 'NoneType'