public boolean isEmpty() {
    return elements.isEmpty();
  }
@Test
  public void testIsEmpty() {
    JsonArray array = new JsonArray();
    assertThat(array).isEmpty();

    JsonPrimitive a = new JsonPrimitive("a");
    array.add(a);
    assertThat(array).isNotEmpty();

    array.remove(0);
    assertThat(array).isEmpty();
  }