'NoMethodError (undefined method `ensure_gitlab_ci_project' for nil:NilClass)' when trying to enable GitLab CI

steps to reproduce

• "Admin area"
• "Service Templates"
• "GitLab CI"
• Tick the "Active" checkbox
• "Save"

backtrace

Processing by Admin::ServicesController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "service"=>{"active"=>"1", "push_events"=>"1", "tag_push_events"=>"1"}, "id"=>"2"}
Completed 500 Internal Server Error in 73ms (ActiveRecord: 6.2ms)

NoMethodError (undefined method `ensure_gitlab_ci_project' for nil:NilClass):
  app/models/project_services/gitlab_ci_service.rb:33:in `ensure_gitlab_ci_project'
  app/controllers/admin/services_controller.rb:16:in `update'

same

Started PUT "/admin/application_settings/services/117" for 127.0.0.1 at 2015-11-23 04:09:19 -0500
Processing by Admin::ServicesController#update as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "service"=>{"active"=>"1", "push_events"=>"1", "tag_push_events"=>"0"}, "id"=>"117"}
Completed 500 Internal Server Error in 70ms (ActiveRecord: 8.7ms)
NoMethodError (undefined method `ensure_gitlab_ci_project' for nil:NilClass):
app/models/project_services/gitlab_ci_service.rb:33:in `ensure_gitlab_ci_project'
app/controllers/admin/services_controller.rb:16:in `update'

mentioned in merge request !1873 (merged)

mentioned in issue #3530 (closed)

Status changed to closed by merge request !1873 (merged)

mentioned in commit 3017037f

mentioned in issue #3670 (closed)

mentioned in commit 2d77a21d

Mentioned in commit maxraab/gitlab-ce@3017037f

mentioned in merge request !14785