Merge branch 'fix-merge-immediately' into 'master'

Fix 'Merge Immediately' button

Fixes #4125

See merge request !2117

app/controllers/projects/merge_requests_controller.rb

@@ -174,7 +174,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     @merge_request.update(merge_error: nil)
-    if params[:merge_when_build_succeeds] && @merge_request.ci_commit && @merge_request.ci_commit.active?
+    if params[:merge_when_build_succeeds].present? && @merge_request.ci_commit && @merge_request.ci_commit.active?
       MergeRequests::MergeWhenBuildSucceedsService.new(@project, current_user, merge_params)
                                                       .execute(@merge_request)
       @status = :merge_when_build_succeeds