My package has said it's NULL at PVG since 8-12. Wondering if my package is stuck in limbo.. My tracking # is RB394172455CN

Unfortunately it's hard to tell exactly what's happening. There are cases where the package is marked as NULL and it's in fact on its way to the country of destination. For other, NULL stays for a week or so and then it's like it goes back to the beginning of the process (opening, etc etc). But hopefully it'll arrive with you soon!