I upgraded liquibase from 3.2.2 to 3.3.2 in order to take advantage of the diffExcludeObjects feature of diffChangeLog.
The first (and every subsequent) run of diffChangeLog after the upgrade resulted in the attached stack trace. I downgraded to 3.3.1 and then 3.3.0 just to see if the exception still occurred, and it did in both of those versions. as well.
This happens regardless of the state of the existing database. I've even run it with bogus db settings, and still get the same error.