Editing a Project Group's name to an empty string generates an exception

To replicate (assuming the user has sufficient roles):

1. Create a project group (name="asdf", id="asdf")
2. Edit a project group, change name into ""

Result:
Caused by: org.codehaus.plexus.rbac.profile.RoleProfileException: invalid role
at org.codehaus.plexus.rbac.profile.AbstractDynamicRoleProfile.renameRole(AbstractDynamicRoleProfile.java:405)
at org.codehaus.plexus.rbac.profile.DefaultRoleProfileManager.renameDynamicRole(DefaultRoleProfileManager.java:134)
at org.apache.maven.continuum.web.action.ProjectGroupAction.save(ProjectGroupAction.java:262)
... 78 more
Caused by: org.codehaus.plexus.security.rbac.RbacObjectInvalidException: Resource.identifier must not be empty.
at org.codehaus.plexus.security.rbac.RBACObjectAssertions.assertValid(RBACObjectAssertions.java:123)
at org.codehaus.plexus.security.rbac.RBACObjectAssertions.assertValid(RBACObjectAssertions.java:110)
at org.codehaus.plexus.security.authorization.rbac.store.jdo.JdoRbacManager.saveResource(JdoRbacManager.java:458)
at org.codehaus.plexus.security.authorization.rbac.store.cached.CachedRbacManager.saveResource(CachedRbacManager.java:662)
at org.codehaus.plexus.rbac.profile.AbstractDynamicRoleProfile.renameRole(AbstractDynamicRoleProfile.java:381)
... 80 more