protected A doBackward(B b) {
      return convert(bimap.inverse(), b);
    }

    private static <X, Y> Y convert(BiMap<X, Y> bimap, X input) {
      Y output = bimap.get(input);
      checkArgument(output != null, "No non-null mapping present for input: %s", input);
      return output;
    }

    @Override
    public boolean equals(@CheckForNull Object object) {