During dbDoc generation liquibase.structure.core.ForeignKey.equals() method throws NPE. This is caused by getPrimaryKeyTable and getPrimaryKeyColumns being null, seems that ForeignKeySnapshotGenerator:87 does not populate these fields at all. As a result when ForeignKey objects are retrieved from HashMap, NPE is thrown.
ForeignKey.equals() should check if these values are null before comparing them (please see attached patch).
SQL Server, Oracle