code: def delete_attribute(key_name)
        key_name_sym = key_name.to_sym
        meta = ensure_metadata_exists(key_name_sym)
        @cache.delete(key_name)
        @writethrough.delete(key_name)
        @source.delete(meta.source_key)
        nil
      end
docs: Delete an attribute
   @param key_name [Symbol] the name of the key
   @return [void]