fix: compilation failure (missing FieldSet.hasProperty())

refs #592

src/app/formulaire/elements/fieldset.ts

@@ -365,6 +365,10 @@ export class FieldSet extends FormulaireElement implements IProperties {
 
     // interface IProperties
 
+    public hasProperty(key: string): boolean {
+        return this._nub.hasProperty(key);
+    }
+
     /**
      * list of properties keys
      */