Migrating database from 3.1 to 4.0 fails while migrating stats on MySQL 5.1

If the database contains stats, the migration fails with a NullPointerException in R40000XWIKI6990DataMigration on line 437 called from line 751. This is due to the fact that the code on line 741 does the following:

Map<Long, Long> map = stats.poll();

and then on line 751:

convertDbId(stats.poll(), new AbstractIdConversionHibernateCallback()

But calling poll() on a LinkedList removes the first item. The call on line 751 should pass the map which was previously removed from the head of the list.