Fixed issue with button color when no CI enabled

Closes #17844

app/assets/javascripts/merge_request_widget.js.coffee

@@ -106,6 +106,7 @@ class @MergeRequestWidget
         @firstCICheck = false
 
   showCIStatus: (state) ->
+    return if not state?
     $('.ci_widget').hide()
     allowed_states = ["failed", "canceled", "running", "pending", "success", "skipped", "not_found"]
     if state in allowed_states
@@ -126,6 +127,6 @@ class @MergeRequestWidget
     $('.ci_widget:visible .ci-coverage').text(text)
 
   setMergeButtonClass: (css_class) ->
-    $('.js-merge-button')
+    $('.js-merge-button,.accept-action .dropdown-toggle')
       .removeClass('btn-danger btn-warning btn-create')
       .addClass(css_class)

app/controllers/projects/merge_requests_controller.rb

@@ -229,6 +229,8 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     if ci_commit
       status = ci_commit.status
       coverage = ci_commit.try(:coverage)
+
+      status ||= "preparing"
     else
       ci_service = @merge_request.source_project.ci_service
       status = ci_service.commit_status(merge_request.last_commit.sha, merge_request.source_branch) if ci_service
@@ -238,8 +240,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
       end
     end
 
-    status = "preparing" if status.nil?
-
     response = {
       title: merge_request.title,
       sha: merge_request.last_commit_short_sha,