Java Either, woo hoo

JEither.java

class JEither<L, R> {

    private L left;
    private R right;

    private JEither() {}

    public <C> C fold(Function<L, C> ifLeft, Function<R, C> ifRight) {
        if (left != null) {
            return ifLeft.apply(left);
        } else {
            return ifRight.apply(right);
        }
    }

    public <C> JEither<L, C> mapRight(Function<R, C> map) {
        return fold(JEither::Left, map.andThen(JEither::Right));
    }

    public <nR> JEither<L, nR> flatMapRight(Function<R, JEither<L, nR>> fmap) {
        return fold(JEither::Left, fmap);
    }

    public static <L, R> JEither<L, R> Left(L value) {
        JEither<L, R> e = new JEither<>();
        e.left = value;
        e.right = null;
        return e;
    }

    public static <L, R> JEither<L, R> Right(R value) {
        JEither<L, R> e = new JEither<>();
        e.left = null;
        e.right = value;
        return e;
    }

}