diff --git a/Server/Controllers/RunController.cs b/Server/Controllers/RunController.cs
index 9ed8786..71789aa 100644
--- a/Server/Controllers/RunController.cs
+++ b/Server/Controllers/RunController.cs
@@ -38,7 +38,7 @@ public async Task<ExecuteResult> EvaluateCellAsync([FromBody] ExecuteRequest cel
                 switch (x)
                 {
                     case DisplayEvent displayEvent:
-                        result.Output = displayEvent.Value;
+                        result.Output = displayEvent.Value?.ToString();
                         break;
                     case CommandFailed commandFailed:
                         result.CommandFailedMessage = commandFailed.Message;