Case showing unexpected behavior when return is missing

missing_error_statement.dart

import 'dart:math';

void main() {
  int rand = Random().nextInt(100);
  print(isEven(rand));
}

String isEven(int number) {
  if (number % 2 == 0) {
    return "Yes. It is even";
  } else {
    "No, it is not even"; // should be an error here
  }
}