code: def _work_path_to_rel_final_path(path, upload_path_mapping, upload_base_dir):
      
      if not path or not isinstance(path, str):
          return path
      upload_path = None
  
      # First, check in the mapping: if it's there is a direct reference and
      # it's a file, we immediately return it (saves lots of iterations)
      if upload_path_mapping.get(path) is not None and os.path.isfile(path):
          upload_path = upload_path_mapping[path]
      else:
          # Not a file: check for elements in the mapping that contain
          # it
          paths_to_check = [key for key in upload_path_mapping
                            if path.startswith(key)]
  
          if paths_to_check:
              for work_path in paths_to_check:
                  if os.path.isdir(work_path):
                      final_path = upload_path_mapping[work_path]
                      upload_path = path.replace(work_path, final_path)
                      break
  
      if upload_path is not None:
          return os.path.relpath(upload_path, upload_base_dir)
      else:
          return None
docs: Check if `path` is a work-rooted path, and convert to a relative final-rooted path