diff --git a/src/WebSocketServer/v1/BlockchainMethods.cs b/src/WebSocketServer/v1/BlockchainMethods.cs
index 18e7b91ac..f2c766c79 100644
--- a/src/WebSocketServer/v1/BlockchainMethods.cs
+++ b/src/WebSocketServer/v1/BlockchainMethods.cs
@@ -198,7 +198,7 @@ public JToken InvokeContract(JArray _params)
 
             try
             {
-                if (_params.Count >= 1 && UInt160.TryParse(_params[0]?.AsString(), out scriptHash))
+                if (_params.Count >= 1 && UInt160.TryParse(_params[0]!.AsString(), out scriptHash))
                 {
                     if (_params.Count >= 2)
                     {