docs: def create(cls, record, bucket):
          """Create a new RecordsBuckets and adds it to the session.
  
          :param record: Record used to relate with the ``Bucket``.
          :param bucket: Bucket used to relate with the ``Record``.
          :returns: The :class:`~invenio_records_files.models.RecordsBuckets`
              object created.
          """
          rb = cls(record=record, bucket=bucket)
          db.session.add(rb)
          return rb