Merge mail not sent - wrong number of arguments (2 for 3)

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After upgrade to 7.14 from 6.7.2 I see in sidekiq.log:

2015-09-18T11:19:48.475Z 7527 TID-or725dqds WARN: {"retry"=>true, "queue"=>"default", "class"=>"Sidekiq::Extensions::DelayedMailer", "args"=>["---\n- !ruby/class 'Notify'\n- :merged_merge_request_email\n- - 3\n  - 357\n"], "jid"=>"2ed99acba74e5a26111b65be", "enqueued_at"=>1442327565.2859857, "error_message"=>"wrong number of arguments (2 for 3)", "error_class"=>"ArgumentError", "failed_at"=>"2015-09-15T14:33:02Z", "retry_count"=>17, "retried_at"=>1442575188.473975}
2015-09-18T11:19:48.475Z 7527 TID-or725dqds WARN: wrong number of arguments (2 for 3)
2015-09-18T11:19:48.475Z 7527 TID-or725dqds WARN: /home/git/gitlab/app/mailers/emails/merge_requests.rb:41:in `merged_merge_request_email'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/actionpack-4.1.11/lib/abstract_controller/base.rb:189:in `process_action'

Is this a misconfiguration, not detected by? :

sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production

PS: have to add, I really like the above test.