ci_build_details_path should return nil if builds_page result is nil

This is required since we parse URI later and remove the credentials

app/helpers/merge_requests_helper.rb

@@ -28,6 +28,8 @@ module MergeRequestsHelper
 
   def ci_build_details_path(merge_request)
     build_url = merge_request.source_project.ci_service.build_page(merge_request.last_commit.sha, merge_request.source_branch)
+    return nil unless build_url
+
     parsed_url = URI.parse(build_url)
 
     unless parsed_url.userinfo.blank?