Fixing the processing GUI so that the null pointer won't happen.  It was because the linkedlist was being polled possibly just after the call to _points.get(0) causing it to return a null element. I suspect the nullPointer is deeper in the stack than that line, but putting synchronized() around _points fixed it just fine.  Also, the linked list can be updated much faster than the teensy can send data back, so something else is causing it to lock up during transfer.