MW 1.27, HHVM 3.14.3.
Warnings in /var/hhvm/error.log on every user login:
\nWarning: trim() expects parameter 1 to be string, null given in /var/www/wiki/w/includes/skins/SkinTemplate.php on line 354
In addition, although the user is logged in, an empty page is often served to him instead of the redirectto page (this could be caused by T140864: Incorrect calls of header () breaks saving some pages).
Also, on any edit action:
\nWarning: htmlspecialchars() expects parameter 1 to be string, null given in /var/www/wiki/w/includes/EditPage.php on line 3045