def get_write_cache(self):
    """Returns the write cache for this setup, creating it if necessary.

    Returns None if no write cache is configured.
    """
    if self._options.write_to and not self._write_cache:
      cache_spec = self._resolve(self._sanitize_cache_spec(self._options.write_to))
      if cache_spec:
        with self._cache_setup_lock:
          self._write_cache = self._do_create_artifact_cache(cache_spec, 'will write to')
    return self._write_cache
Returns the write cache for this setup, creating it if necessary.

    Returns None if no write cache is configured.