TD-4889 Fixing internal server error

Author: sherif-olaboye

DigitalLearningSolutions.Web/Controllers/SupervisorController/Supervisor.cs

@@ -1304,7 +1304,7 @@ public IActionResult ConfirmNominateSupervisor(SupervisorDelegateViewModel super
                     supervisorDelegateDetail.DelegateUserID,
                     (int)User.GetCentreId()
                 );
-                supervisorDelegate.SelfAssessmentCategory = supervisorDelegate.SelfAssessmentCategory == 0   ? adminUser.CategoryId.Value  : supervisorDelegate.SelfAssessmentCategory;
+                supervisorDelegate.SelfAssessmentCategory = supervisorDelegate.SelfAssessmentCategory == 0 ? (adminUser.CategoryId.HasValue ? adminUser.CategoryId.Value : 0) : supervisorDelegate.SelfAssessmentCategory;
                 var centreName = adminUser.CentreName;
 
                 var adminRoles = new AdminRoles(false, false, true, false, false, false, false, false);