Flutter pubspec.yaml null sfety error solution
The lower bound of "sdk: '>=2.5.0 <3.0.0'" must be 2.12.0 or higher to enable null safety. I resolve this by: flutter pub upgrade --major-versions the other 2 code I run erlier is: flutter pub get and flutter pub get --no example Which both resulting in error. The code : flutter pub upgrade --major-versions is recommmend by terminal to resolve my issue. and all error on lib folder gone.