public Expression getAttributeUndefinedValue(Factory factory) {
	if (attrUndefinedValue == null) return factory.TRUE();
	return factory.createLiteral(attrUndefinedValue, factory.TRUE());
    }
public Expression getAttributeUndefinedValue ( Factory factory ) { if ( attrUndefinedValue == null ) return factory . TRUE ( ) ; return factory . createLiteral ( attrUndefinedValue , factory . TRUE ( ) ) ; }
attribute value set, if the attribute has no value defined

@return