@CanIgnoreReturnValue
  @Override
  public JsonWriter beginObject() throws IOException {
    JsonObject object = new JsonObject();
    put(object);
    stack.add(object);
    return this;
  }
@Test
  public void testBeginObject() throws Exception {
    JsonTreeWriter writer = new JsonTreeWriter();
    assertThat(writer.beginObject()).isEqualTo(writer);
  }