cannot create wiki pages outside of my namespace starting with v8.7.0

Hi,

I'm using Gitlab CE v8.7.0 with LDAP authentication. Starting with v8.7.0, I'm not able to create or edit wiki pages outside of my own namespace. Whenever I try to create a new wiki page in a wiki of a group I have 'master' privileges in, I get an error 500. This is the related log entry in the production.log:

Started POST "/test/dummy/wikis" for 127.0.0.1 at 2016-04-28 10:26:36 +0200
Processing by Projects::WikisController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "wiki"=>{"title"=>"home", "format"=>"markdown", "content"=>"test", "message"=>""}, "namespace_id"=>"test", "project_id"=>"dummy"}
Completed 200 OK in 103ms (Views: 0.5ms | ActiveRecord: 6.9ms)
Completed 500 Internal Server Error in 94ms (ActiveRecord: 7.9ms)
NoMethodError (undefined method `username' for #<Group:0x00000008f591c0>):

Before the upgrade, when using v8.6.x, it worked flawlessly.