}

    @Override
    public String toString() {
      return adder.toString();
    }
  }

  private static class FailsToPropagateException implements Adder {
    private final Adder adder;

    FailsToPropagateException(Adder adder) {
      this.adder = adder;
    }

    @Override
    @SuppressWarnings("CatchingUnchecked") // sneaky checked exception

    }

    @Override
    public String toString() {
      return adder.toString();
    }
  }

  private static class FailsToPropagateException implements Adder {
    private final Adder adder;

    FailsToPropagateException(Adder adder) {
      this.adder = adder;
    }

    @Override
    @SuppressWarnings("CatchingUnchecked") // sneaky checked exception