Short answer: Instead of the pre-null-safety operations var foo = List<int>(); // Now error var bar = List<int>(n); // Now error var baz = List<int>(0); // Now error use the following: var foo = <int>[]; // Always the recommended way. var bar = List.filled(1, 0); // Not filled with `null`s. var baz = List<int>.empty(); Long … Read more
Welcome to Dart. What you are experience is the new null-safety feature (introduced with Dart 2.12.0) where variables by default cannot contain the value null. This is statically checked so you will get an error even before your program are executed. In your example the problem is the following line: var input = stdin.readLineSync(); If … Read more
Don’t downgrade Flutter Problem: This error occurs when you use a bang operator (!) on a nullable instance which wasn’t initialized. For example: String? foo; // Nullable String void main() { var len = foo!.length; // Runtime error: Null check operator used on a null value } Solutions: You need to find out where you’re … Read more
Dart engineer Erik Ernst says on GitHub: Type promotion is only applicable to local variables. … Promotion of an instance variable is not sound, because it could be overridden by a getter that runs a computation and returns a different object each time it is invoked. Cf. dart-lang/language#1188 for discussions about a mechanism which is … Read more