OnInstallation nullable

Author: ThomasArdal

src/Elmah.Io.OpenTelemetry/ElmahIoExporterOptions.cs

@@ -34,7 +34,7 @@ public class ElmahIoExporterOptions
         /// Register an action to be called before creating an installation. Use the OnInstallation
         /// action to decorate installations with additional information related to your environment.
         /// </summary>
-        public Action<CreateInstallation> OnInstallation { get; set; }
+        public Action<CreateInstallation>? OnInstallation { get; set; }
 
         /// <summary>
         /// Register an action to be called if communicating with the elmah.io API fails.