private Widget literalEditor() {
//Custom screen
if ( this.constraint instanceof SingleFieldConstraint ) {
final SingleFieldConstraint con = (SingleFieldConstraint) this.constraint;
CustomFormConfiguration customFormConfiguration = WorkingSetManager.getInstance().getCustomFormConfiguration( modeller.getAsset().getMetaData().getPackageName(),
factType,
fieldName );
if ( customFormConfiguration != null ) {
Button btnCustom = new Button( con.getValue(),
new ClickHandler() {