func (n NullDuration) MarshalJSON() ([]byte, error) {
	if !n.Valid {
		return []byte("null"), nil
	}

	return json.Marshal(n.Duration)
}
// MarshalJSON - marshaller for json
marshaller for json
// MarshalJSON - marshaller for json
func (n NullDuration) MarshalJSON() ([]byte, error) {
	if !n.Valid {
		return []byte("null"), nil
	}
	return json.Marshal(n.Duration)
}
func ( n NullDuration ) MarshalJSON ( ) ( [ ] byte , error ) { if ! n . Valid { return [ ] byte ( " " ) , nil } return json . Marshal ( n . Duration ) }
marshaller for json
marshaller for json