Uninitialized variable error message leaks information

How it was found

An uninitialized variable $alert at line 630 in index.php shows an error message. This happens after a POST /pages/create_project. The error message does not appear in the browser because the user is redirected to the new project immediately, but it is there in the HTTP response (see error.png).

This is probably fixed with something like this at line 630. if(isset($alert)) echo UI::getPage(UI::PAGE_CREATE_PROJECT, array($alert));