Query Issues by labels after upgrading from 4.0.1 to 4.2.4

Before the upgrade from 4.0.1 to 4.2.4 using Jira Labels Plugin, the following query works:

project = MB and fixVersion = "Maint 3 - May 2011 Version 2.2.2" and label not in (core_integration, android_stopgap)

This will show all the issues with the exception of the Core Integration and the Android Stop Gap work labels. The not labeled issues will be displayed as well.

After the upgrade all the tickets that had no label had also been excluded. re-wroting the query as the following:

project = mb and fixVersion = "Maint 3 - May 2011 Version 2.2.2" and (label not in (Core_Integration, Android_Stopgap) or label is EMPTY)

Then it will pull the non-labeled issues also