controller might not exist (such as in the case of Rails default 404 handling)

Author: bknoles

lib/inertia_rails/middleware.rb

@@ -78,7 +78,7 @@ def version_stale?
       end
 
       def server_version
-        controller.send(:inertia_configuration).version
+        controller&.send(:inertia_configuration)&.version
       end
 
       def coerce_version(version)