Optional.ofNullable(order.getCurrency()).orElse("USD");

Optional.ofNullable(params.get("abc")).orElseThrow(() -> new IllegalArgumentException(message));

public interface User {
  String name();
  Integer age();

  User EMPTY = new User() {
     @Override
     public String name() {
            return "";
     }
     @Override
     public Integer age() {
            return 0;
     }
  };
}

Optional.ofNullable(user).orElse(User.EMPTY)