diff --git a/lib/src/core/implementation/interaction_output.dart b/lib/src/core/implementation/interaction_output.dart
index 54776ac6..89ab1a55 100644
--- a/lib/src/core/implementation/interaction_output.dart
+++ b/lib/src/core/implementation/interaction_output.dart
@@ -20,13 +20,15 @@ class InteractionOutput implements scripting_api.InteractionOutput {
   /// payload contained in the [Content] object.
   InteractionOutput(
     this._content,
-    this._contentSerdes, [
+    this._contentSerdes,
     this._form,
     this._schema,
-  ]) : _data = _content.body;
+  ) : _data = _content.body;
 
   final Content _content;
-  final Form? _form;
+
+  final Form _form;
+
   final DataSchema? _schema;
   final Stream<List<int>> _data;
 
@@ -76,5 +78,5 @@ class InteractionOutput implements scripting_api.InteractionOutput {
   DataSchema? get schema => _schema;
 
   @override
-  Form? get form => _form;
+  Form get form => _form;
 }
diff --git a/test/core/interaction_output_test.dart b/test/core/interaction_output_test.dart
index 1c53e745..ee3780ed 100644
--- a/test/core/interaction_output_test.dart
+++ b/test/core/interaction_output_test.dart
@@ -27,7 +27,7 @@ void main() {
       final interactionOutput = InteractionOutput(
         content,
         contentSerdes,
-        null,
+        Form(Uri.parse("http://example.org")),
         const DataSchema(),
       );
 
@@ -54,7 +54,7 @@ void main() {
       final interactionOutput = InteractionOutput(
         content,
         contentSerdes,
-        null,
+        Form(Uri.parse("http://example.org")),
         const DataSchema(),
       );