public static <T> RuntimeTypeAdapterFactory<T> of(
      Class<T> baseType, String typeFieldName, boolean maintainType) {
    return new RuntimeTypeAdapterFactory<>(baseType, typeFieldName, maintainType);
  }
@Test
  public void testNullBaseType() {
    assertThrows(NullPointerException.class, () -> RuntimeTypeAdapterFactory.of(null));
  }