Can you explain the principle of the null reference protection system in programming languages?

In the Dart language, used in Flutter, a null safety system is implemented — a mechanism that prevents errors related to null references. The idea is that variables by default cannot hold null values unless explicitly specified.

This is achieved through strict typing and special operators:

• Types without a question mark (e.g., int, String) cannot be null.
• Types with a question mark (e.g., int?, String?) can contain null.
• The ! operator (null assertion) indicates that the value is definitely not null, but an exception will be thrown if it is.
• The ?. operator allows safe access to object members if the object is not null.

Example:

String? name; // can be null

void printNameLength() {
  if (name != null) {
    print(name!.length); // safe, since we checked
  } else {
    print('Name is null');
  }
}

Thus, the compiler helps identify potential null errors at compile time, reducing runtime errors.