def content_mimetype_missing(self, mimetypes, db=None, cur=None):
        """Generates mimetypes missing from storage.
        
        Args:
            mimetypes (iterable): iterable of dict with keys:

              :id (bytes): sha1 identifier
              :indexer_configuration_id (int): tool used to compute the results

        Yields:
            tuple (id, indexer_configuration_id): missing id

        """