return this;
    }

    private UnconditionalValueHolder addUnconditionalHolder() {
      UnconditionalValueHolder valueHolder = new UnconditionalValueHolder();
      holderTail = holderTail.next = valueHolder;
      return valueHolder;
    }

    @CanIgnoreReturnValue
    private ToStringHelper addUnconditionalHolder(Object value) {
      UnconditionalValueHolder valueHolder = addUnconditionalHolder();