diff --git a/BetterIServ.Backend/Controllers/UnitsController.cs b/BetterIServ.Backend/Controllers/UnitsController.cs
index 5f01f82..0fd0271 100644
--- a/BetterIServ.Backend/Controllers/UnitsController.cs
+++ b/BetterIServ.Backend/Controllers/UnitsController.cs
@@ -56,6 +56,8 @@ public class UnitsController : ControllerBase {
 
             if (!classes.StartsWith("Q")) {
                 string grade = new string(classes.ToCharArray().Where(char.IsNumber).ToArray());
+                if (string.IsNullOrEmpty(grade)) break;
+
                 var subClasses = classes.Replace(grade, "").ToCharArray();
                 var result = new string[subClasses.Length];