[xbase][trace] Don’t skip empty root regions

We need to store the path information for the tracing to
work properly.

see https://bugs.eclipse.org/bugs/show_bug.cgi?id=448020

Change-Id: I79185f5281269d67e13a581c158b5401944402d7
[xbase][validation] Avoid NPE since it’ll break the final field init check

Change-Id: I8e8a1db287f138bb9d7acc6927bae5d89985108c