diff --git a/src/Squidex.Infrastructure/Json/Objects/JsonObject.cs b/src/Squidex.Infrastructure/Json/Objects/JsonObject.cs
index c4974ce47..6eb6195d0 100644
--- a/src/Squidex.Infrastructure/Json/Objects/JsonObject.cs
+++ b/src/Squidex.Infrastructure/Json/Objects/JsonObject.cs
@@ -24,7 +24,7 @@ namespace Squidex.Infrastructure.Json.Objects
             }
             set
             {
-                Guard.NotNullOrEmpty(key, nameof(key));
+                Guard.NotNull(key, nameof(key));
 
                 inner[key] = value ?? JsonValue.Null;
             }