code: def create_backend_noexc(log: logging.Logger, name: str=None, git_index: GitIndex=None,
                           args: str=None) -> Optional[StorageBackend]:
      
      try:
          return create_backend(name, git_index, args)
      except KeyError:
          log.critical("No such backend: %s (looked in %s)",
                       name, list(__registry__.keys()))
          return None
      except ValueError:
          log.critical("Invalid backend arguments: %s", args)
          return None
docs: Initialize a new Backend, return None if there was a known problem.