fix: defensive guard added against jumpDisputeKitID not set

Author: jaybuidl

contracts/src/arbitration/KlerosCoreBase.sol

@@ -1081,8 +1081,8 @@ abstract contract KlerosCoreBase is IArbitratorV2, Initializable, UUPSProxiable
         if (!courts[newCourtID].supportedDisputeKits[newDisputeKitID]) {
             // The current Dispute Kit is not compatible with the new court, jump to another Dispute Kit.
             newDisputeKitID = disputeKits[_round.disputeKitID].getJumpDisputeKitID();
-            if (!courts[newCourtID].supportedDisputeKits[newDisputeKitID]) {
-                // The new Dispute Kit is still not compatible, fall back to `DisputeKitClassic` which is always supported.
+            if (newDisputeKitID == NULL_DISPUTE_KIT || !courts[newCourtID].supportedDisputeKits[newDisputeKitID]) {
+                // The new Dispute Kit is not defined or still not compatible, fall back to `DisputeKitClassic` which is always supported.
                 newDisputeKitID = DISPUTE_KIT_CLASSIC;
             }
             disputeKitJump = true;