}

  private static class StringHolder {
    @Nullable String string;
  }

  @SuppressWarnings("JUnitIncompatibleType")
  public void testBuilder_withMutableEntry() {
    ImmutableMultimap.Builder<String, Integer> builder = new Builder<>();
    StringHolder holder = new StringHolder();
    holder.string = "one";
    Entry<String, Integer> entry =