Manual talk:Skinning/Vector

I have duplicated folder "/skins/vector" into "/skins/foobar", then duplicated files Vector.php and Vector.deps.php into FooBar.php and FooBar.deps.php and after that changed the mentioned in manual words in FooBar.php and added a code $wgResourceModules['skins.runavector'] = array(...); just after the "if !defined (' MEDIAWIKI' ){...} And I've got en error "Call to a member function getGroup on a non-object in /var/www/runa/includes/OutputPage.php on line 2707". How can I fix that error?