Видео ютуба по тегу Non-Nullable Instance Field ['Controller'] Must Be Initialized In Flutter

Null problem In Dart |Non-nullable instance field must be initialized | Error in Dart Language
Null problem In Dart |Non-nullable instance field must be initialized | Error in Dart Language
Solve the Non-nullable instance field ['controller'] must be initialized in Flutter Error
Solve the Non-nullable instance field ['controller'] must be initialized in Flutter Error