code: func (b *lowBuilder) sortedDBMS(named dbname) (map[string]interface{}, error) {
  	if b.high.MySQL != "" {
  		return b.dbIndexStorage("mysql", b.high.MySQL, named)
  	}
  	if b.high.PostgreSQL != "" {
  		return b.dbIndexStorage("postgres", b.high.PostgreSQL, named)
  	}
  	if b.high.Mongo != "" {
  		return b.mongoIndexStorage(b.high.Mongo, named)
  	}
  	return nil, nil
  }
docs: // sortedDBMS returns the configuration for a name database on one of the
  // DBMS, if any was found in the configuration. It returns nil otherwise.