source: class DDRJSONUtilsTest {
  
      @Test
      public void test01() {
  
target:         List<String> list = new ArrayList<>();
          list.add("12");
          list.add("34");
          list.add(null);
          String src = DDRJSONUtils.toJSONString(list);
          Assert.equals(src, "[\"12\",\"34\",null]");
      }
  
  }