code: func (t *Transaction) SelectNullStr(query string, args ...interface{}) (sql.NullString, error) {
  	if t.dbmap.ExpandSliceArgs {
  		expandSliceArgs(&query, args...)
  	}
  
  	return SelectNullStr(t, query, args...)
  }
docs: // SelectNullStr is a convenience wrapper around the gorp.SelectNullStr function.