ERROR:flutter/lib/ui/ui_dart_state.cc(148) Unhandled Exception

I faced a similar problem when I migrated Flutter from 1.0.3 to 1.2.1. What I found out the problem is related to the parameter defined on the void main method. Those parameters are never passed when main is called. To fix this you can remove those params and make the following changes to the other places where it's being used.

void main() async {
.
.
.
  runZoned<Future<Null>>(() async {
    runApp(ReduxApp());
.
.
.
  ReduxApp({
    Key key})  : store = Store<AppState>(
          appReducer,
          initialState: AppState.initial(),
          middleware: createStoreTodosMiddleware(
            FirestoreReactiveTodosRepository(Firestore.instance),
            FirestoreReactiveFeedsRepository(Firestore.instance),
            FirestoreReactiveUserFeedsRepository(Firestore.instance),
            AuditAPIRepository(),
            FirebaseUserRepository(FirebaseAuth.instance),
            SCUserRepositoryImpl(),
          ),
.
.
.

This is a type mismatch error make sure your return type is same as the variable type