In Dart, when you opt into null safety, types are non-nullable by default, meaning that values can't be null unless you explicitly say they can be[1][3]. This design principle was chosen after research found that non-null was by far the most common choice in APIs[3].
Some key points about non-nullable by default in Dart:
Unless you add a ? after a type to make it nullable, variables are considered non-nullable[1][3]. For example, int is non-nullable, while int? is nullable.
Non-nullable variables must be initialized with a non-null value before they can be used[3]. The Dart analyzer enforces this.
Assigning null to a non-nullable variable results in a compile-time error[3]. This prevents null dereference errors at runtime.
The default for parameters, return types, fields, a...
