diff --git a/contract/Forest/ForestContract_Views.cs b/contract/Forest/ForestContract_Views.cs
index b8881ad..f23524e 100644
--- a/contract/Forest/ForestContract_Views.cs
+++ b/contract/Forest/ForestContract_Views.cs
@@ -130,8 +130,8 @@ public override GetTotalEffectiveListedNFTAmountOutput GetTotalEffectiveListedNF
                 TotalAmount = totalAmount
             };
         }
-        
-        if (allowance != 0 && collectionAllowance == "")
+
+        if (allowance != 0 && (collectionAllowance == null || collectionAllowance == ""))
         {
             return new GetTotalEffectiveListedNFTAmountOutput()
             {