SPWeb.RootFolder.WelcomePage not working

You cannot set the welcome page of a non publishing site with the following code :

teamWeb.RootFolder.WelcomePage = rootFolder.Name + "/" + myPage;
teamWeb.RootFolder.Update();

Don't know the exact reason why it will not work.

But it will not work as it expected to work on.

Here is the code which you can set the welcome page of a non publishing site.

You can set this only with the SPFOlder object, Then only it will work.

SPFolder folder = context.Web.RootFolder;
folder.WelcomePage = rootFolder.Name + "/" + myPage;
folder.Update();

Thank you !!