Traceback (most recent call last):
  File "/usr/bin/snapcraft", line 31, in <module>
    snapcraft.main.main()
  File "/usr/lib/python3/dist-packages/snapcraft/main.py", line 230, in main
    return run(args, project_options)
  File "/usr/lib/python3/dist-packages/snapcraft/main.py", line 288, in run
    lifecycle.snap(project_options, args['<directory>'], args['--output'])
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 316, in snap
    snap = execute('prime', project_options)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 100, in execute
    config = snapcraft.internal.load_config(project_options)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/project_loader.py", line 357, in load_config
    return Config(project_options)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/project_loader.py", line 145, in __init__
    self._snapcraft_yaml)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/parts.py", line 163, in __init__
    self._process_parts()
  File "/usr/lib/python3/dist-packages/snapcraft/internal/parts.py", line 186, in _process_parts
    self.load_plugin(part_name, plugin_name, properties)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/parts.py", line 263, in load_plugin
    part_schema=self._validator.part_schema)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/pluginhandler.py", line 776, in load_plugin
    part_schema=part_schema)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/pluginhandler.py", line 105, in __init__
    self._load_code(plugin_name, self._part_properties, part_schema)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/pluginhandler.py", line 133, in _load_code
    _validate_pull_and_build_properties(plugin_name, plugin, part_schema)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/pluginhandler.py", line 667, in _validate_pull_and_build_properties
    part_schema, plugin.schema())
  File "/usr/lib/python3/dist-packages/snapcraft/internal/pluginhandler.py", line 656, in _merged_part_and_plugin_schemas
    plugin_schema = plugin_schema.copy()
AttributeError: 'NoneType' object has no attribute 'copy'