diff --git a/lib/csharp/src/TException.cs b/lib/csharp/src/TException.cs
index aa9a210..b9fae6e 100644
--- a/lib/csharp/src/TException.cs
+++ b/lib/csharp/src/TException.cs
@@ -31,7 +31,7 @@
         {
         }
 
-        public TException(string message, Exception inner)
+        public TException(string message, Exception inner = null)
             : base(message, inner)
         {
         }