fix: handle null workshop details in ticket display logic

CompanyManagment.Application/WorkshopAppliction.cs

@@ -407,6 +407,10 @@ public class WorkshopAppliction : IWorkshopApplication
     public EditWorkshop GetDetails(long id)
     {
         var workshop = _workshopRepository.GetDetails(id);
+        if (workshop == null)
+        {
+            return null;
+        }
         if (workshop.IsClassified)
         {
             workshop.CreatePlan = _workshopPlanApplication.GetWorkshopPlanByWorkshopId(id);