Oops fix #459 (for real)

src/app/formulaire/elements/formulaire-node.ts

@@ -161,7 +161,9 @@ export abstract class FormulaireNode implements IObservable {
             }
         }
         // restore original calculated param
-        calcP.setCalculated();
+        if (calcP !== undefined) {
+            calcP.setCalculated();
+        }
     }
 
     /**