Handle accidental null arguments to Trace APIs.

We have @NonNull annotations, but not everyone is watching the warning
messages related to them.  Make the implementation a bit more robust
by swapping in the "(null)" literal when someone accidentally leaks
one through.

Bug: 249325721
Test: atest FrameworksCoreTests:TraceTest
Change-Id: Ic0f5a0236fbce88e086f3d68b2e5c6ed6b0aa33c