a Json::Value container.

Value is not a container. They're only valid if the Value is holding an array.
If the Value is holding an object, or anything scalar, this will fail, right?

It should actually still be valid if Value is holding an object, since the iterator returned by Value::begin() is also valid for objects.
But, yes, for scalars it is undefined behavior as to what will happen, since you're trying to dereference a default constructed ValueIterator (or ConstValueIterator).
I didn't add an assertion, since it seemed like this is the preferred style, due to the fact that Value::begin() also just returns a default constructed iterator, which, when dereferenced, will fail.

@BillyDonahue Does the previous comment answer your question?

Thank you! LGTM

@BillyDonahue What's the status on this? Is it still something you'd be interested in getting in?

I guess it's safe to say Travis CI isn't going to finish :)