Nullable Strings?

[nikeee]

Consider this JSON document:

{"foo": null }

The foo property is either a string or null.
When I try the following:

String json = "{\"foo\": null }";
JsonObject obj = new JsonObject().withValue(json);
String foo = obj.getString("foo");

I expected foo to be null, not "".

How to distinguish "foo": null from "foo": ""?
I looked up how org.json handles this case. As stated here, it behaves similar:
http://stackoverflow.com/questions/13118146

However, org.json provides an isNull method. Since there are no docs for the NetworkParser, I ended up looking in the source, ending up with nothing.

That leaves me with the question:
How to distinguish between "" and null using the NetworkParser library when using getString?

Edit:
I am currently using this workaround:

String nullable = (String)obj.get("foo");

However, considering this JSON document: {"foo": 5 }, the cast to String will fail because get() returns the int 5 (which seems good to me), whereas getString() returns "5" in this case.