DartにおけるNullチェック、isEmpty、isNotEmptyの振る舞い

テストコード

main.dart
void main() {
  String? testDataNull = null;
  String? testDataEmptyString = "";
  String? testDataString = "testData";
  
  print("testDataNull == null: ${testDataNull == null}");
  print("testDataNull != null: ${testDataNull != null}");
  print("testDataNull.isEmpty: ${testDataNull?.isEmpty}");
  print("testDataNull.isNotEmpty: ${testDataNull?.isNotEmpty}");
  
  print("--------------------------------");
  
  print("testDataEmptyString == null: ${testDataEmptyString == null}");
  print("testDataEmptyString != null: ${testDataEmptyString != null}");
  print("testDataEmptyString.isEmpty: ${testDataEmptyString?.isEmpty}");
  print("testDataEmptyString.isNotEmpty: ${testDataEmptyString?.isNotEmpty}");
  
  print("--------------------------------");
  
  print("testDataString == null: ${testDataString == null}");
  print("testDataString != null: ${testDataString != null}");
  print("testDataString.isEmpty: ${testDataString?.isEmpty}");
  print("testDataString.isNotEmpty: ${testDataString?.isNotEmpty}");
}