Steps to reproduce

1. Create two Crucible project: ProjectA and ProjectB
2. Create a group GroupA with member 'UserA'
3. Set GroupA as the Allowed review participants for ProjectA
4. Create a review in ProjectB without any reviewer
5. Migrate the review in ProjectB to ProjectA
   Unable to migrate to review to ProjectA with the following error in the log:

   2014-05-21 18:29:21,614 WARN  [qtp1498068251-146 ] org.eclipse.jetty.servlet.ServletHandler ServletHandler-doHandle - /json/cru/asdf-2/postDetails
   java.lang.NullPointerException
   	at com.cenqua.crucible.model.managers.impl.DefaultProjectManager.isAllowedReviewer(DefaultProjectManager.java:426)
   	at com.cenqua.crucible.model.managers.impl.DefaultProjectManager.moveReviewInternal(DefaultProjectManager.java:304)
   	at com.cenqua.crucible.model.managers.impl.DefaultProjectManager.moveReviewToProject(DefaultProjectManager.java:288)
   	at com.atlassian.crucible.actions.create.EditReviewDetailsAction.execute(EditReviewDetailsAction.java:397)
   	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   

Workaround

Remove all the group in Allowed review participants before migrating the review