<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def create_backend_noexc(log: logging.Logger, name: str=None, git_index: GitIndex=None, args: str=None) -> Optional[StorageBackend]: """Initialize a new Backend, return None if there was a known problem."""

    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