Errors in site_cubicweb.py

    add_mappers_to_cube_appobject_path()
  File "/home/katia/.virtualenvs/siaf4.2/lib/python3.9/site-packages/cubicweb_jsonschema/site_cubicweb.py", line 52, in add_mappers_to_cube_appobject_path
    LOGGER.warning(
Message: 'failed to import %s.%s, "mappers" appobjects will not loaded for this configuration'

  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/home/katia/src/siafcw28/jsonschema/cubicweb_jsonschema/site_cubicweb.py", line 59, in <module>
    add_mappers_to_cube_appobject_path()
  File "/home/katia/src/siafcw28/jsonschema/cubicweb_jsonschema/site_cubicweb.py", line 51, in add_mappers_to_cube_appobject_path
    LOGGER.warning(
Message: 'failed to import %s.%s, "mappers" appobjects will not loaded for this configuration'
Arguments: (('cubicweb.server.serverconfig', 'ServerConfiguration'),)