Null Safety

Null safety is one of Dart's most important features. By default, it stops a variable from ever becoming null. It catches the 'using a value that doesn't exist' problem — the kind that crashes apps — early.

void main() {
  String name = 'Dart';
  // name = null; // Error: non-nullable variable

  String? nickname;
  nickname = null;

  print(name.length);
  print(nickname?.length ?? 0);
}

String name can never be null. String? is nullable — it can be null. ?. only accesses the property if a value exists, and ?? provides a default value when it's null.

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