Working

lib/controllers/registration_controller.dart

@@ -0,0 +1,15 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:nexusbot/models/registration.dart";
+import "package:riverpod/riverpod.dart";
+
+class RegistrationController extends Notifier<IList<Registration>> {
+  @override
+  IList<Registration> build() => const IList.empty();
+
+  void add(Registration registration) => state = state.add(registration);
+
+  static final provider =
+      NotifierProvider<RegistrationController, IList<Registration>>(
+        RegistrationController.new,
+      );
+}