final String result = MoreObjects.toStringHelper(new TestClass()).add("Hello", null).toString();

    assertEquals("TestClass{Hello=null}", result);
  }

  public void testToStringLenient_addWithNullValue() {
    final String result = MoreObjects.toStringHelper(new TestClass()).add("Hello", null).toString();
    assertTrue(result, result.matches(".*\\{Hello\\=null\\}"));
  }