def exists_locally?(key_name)
      return true if @cache.key?(key_name) || @writethrough.key?(key_name)
      meta = ensure_metadata_exists(key_name)
      @source.key?(meta.source_key)
    end
def exists_locally?(key_name)
      return true if @cache.key?(key_name) || @writethrough.key?(key_name)
      meta = ensure_metadata_exists(key_name)
      @source.key?(meta.source_key)
    end
Whether the key doesn't need to be lazily loaded.
 @param key_name [Symbol] the key to check
 @return [Boolean] whether the key exists locally.