public function changeLog($output = null, $metadata = null)
    {
        $output = $this->sanitizeOutputParameter($output);
        $metadata = $this->sanitizeMetadatas($metadata);

        $schema = $this->getSchemaFromMetadata($metadata);
        $liquibaseVisitor = new LiquibaseSchemaVisitor($output);
        $output->started($this->em);
        $schema->visit($liquibaseVisitor);
        $output->terminated();

        return $output->getResult();
    }