Java :: Handle Nullable Integer - Flex Remoting Application?

I have an Application consisting of a Java Server part and a Flash/Flex client, both communicate via BlazeDS. In order to have the same typed Objects on both sites, I use the GAS3 code generator (used by flex-mojos).But now I am facing the problem of handling nullable Integers. The problem is that I have an Object (A) which contains a foreign key ID which is reference an optional Object B. - But I only send the ID to the flex client.On the Java site it is easy:

class A {
private Integer bFk;
getter/setter
}

But on the flex client side, bFk is of type int. And a Flash int can not be null. So the remoting mechanism converts the Java null Integer to 0. After sending it back to the server, the Java bFk becomes 0 even on the Java side. - That is not acceptable, because I need to separate 0 and nullMy first workround is using not a Integer on the Java side, but an new Class NullAbleID, which works a bit like a wrapper/adapter, that wrap an internal int where -1 represent null (I can use -1 for null, because real id will be negative). But when I would using this it means I have to replace all Java Integer ids, by this NullAbleID class.