Merge Request CI Status

Problem: When GitLab CI is enabled and properly configured the merge request integration with GitLab CI is not properly getting the build status.

GitLab 7.6.2

GitLab Shell 2.4.0

GitLab API v3

Ruby 2.1.4p265

Rails 4.1.1

GitLab CI 5.3.0 (6465f27)

Started GET "/preston/hedwig/merge_requests/36/ci_status" for ... at 2015-01-12 10:16:42 -0500
Processing by Projects::MergeRequestsController#ci_status as JSON
Parameters: {"project_id"=>"preston/hedwig", "id"=>"36"}
Completed 500 Internal Server Error in 71ms
NoMethodError (undefined method `commit_status' for nil:NilClass):
app/controllers/projects/merge_requests_controller.rb:146:in `ci_status'

Might be related to #883 (closed)