diff --git a/packages/dev-tools/lib/DevTools.ts b/packages/dev-tools/lib/DevTools.ts
index 0d4aaff..01531de 100644
--- a/packages/dev-tools/lib/DevTools.ts
+++ b/packages/dev-tools/lib/DevTools.ts
@@ -232,7 +232,8 @@ export function getMockMediatorExpressionEvaluatorFactory(
 ): MediatorExpressionEvaluatorFactory {
   return <any>{
     async mediate(arg: any) {
-      return getMockEEFactory(args).run(arg);
+      // eslint-disable-next-line unicorn/no-useless-undefined
+      return getMockEEFactory(args).run(arg, undefined);
     },
   };
 }