default B applyOrElse(A x, Function<? super A, ? extends B> that) {
        return isDefinedAt(x) ? apply(x) : that.apply(x);
    }
Work exactly same as scala's PartialFunction.

@param <A> argument type
@param <B> result type
indexr-common/src/main/java/io/indexr/util/function/PartialFunction.java