'Creates and returns a minimal BlockData object with the give value
for explicit_graded.'

def _create_block(self, explicit_graded_value):

    block = BlockData('any_key')
    setattr(block.transformer_data.get_or_create(GradesTransformer), GradesTransformer.EXPLICIT_GRADED_FIELD_NAME, explicit_graded_value)
    return block
