IIS Rewrite does not work for the root of an application

With IIS7, URL Rewrite 2 there is an MVC4 application APP on server SRV. The following rewrite should happen.
http://SRV/APP into http://SRV/APP/ I tried by creating the AddTrailingSlash rule. However, it does not work for the application's root. It does work for directories under the root, so the following rewrite is done
http://SRV/APP/pipapo into http://SRV/APP/pipapo/ What has to be done so the rewrite also works for the root?
Michael G. Schneider
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