"Value cannot be null" on references tab in Resource Properties Dialog

[jng]

Bring up the resource references tab on the properties for an Application Definition. Maestro errors out with the following:

System.ArgumentNullException: Value cannot be null.
Parameter name: identifier
   at OSGeo.MapGuide.MaestroAPI.Resource.ResourceIdentifier.GetExtension(String identifier) in c:\Program Files (x86)\Jenkins\jobs\Maestro trunk\workspace\OSGeo.MapGuide.MaestroAPI\Resource\ResourceIdentifier.cs:line 401
   at OSGeo.MapGuide.MaestroAPI.Resource.ResourceIdentifier.GetResourceType(String identifier) in c:\Program Files (x86)\Jenkins\jobs\Maestro trunk\workspace\OSGeo.MapGuide.MaestroAPI\Resource\ResourceIdentifier.cs:line 390
   at Maestro.Base.UI.ResourceIconCache.GetImageIndexFromResourceID(String resourceId) in c:\Program Files (x86)\Jenkins\jobs\Maestro trunk\workspace\Maestro.Base\UI\ResourceIconCache.cs:line 142
   at Maestro.Base.UI.ResourcePropertiesDialog.ReferenceWorker_RunWorkerCompleted(Object sender, RunWorkerCompletedEventArgs e) in c:\Program Files (x86)\Jenkins\jobs\Maestro trunk\workspace\Maestro.Base\UI\ResourcePropertiesDialog.cs:line 945
   at System.ComponentModel.BackgroundWorker.OnRunWorkerCompleted(RunWorkerCompletedEventArgs e)
   at System.ComponentModel.BackgroundWorker.AsyncOperationCompleted(Object arg)

[jng]

Fixed trunk (r7293) and 4.0.x (r7294)