Move conditional statement to PipelineSerializer#represent_status

app/controllers/projects/merge_requests_controller.rb

@@ -474,7 +474,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def pipeline_status
-    render json: {} and return unless @merge_request.head_pipeline.present?
     render json: PipelineSerializer
       .new(project: @project, user: @current_user)
       .represent_status(@merge_request.head_pipeline)

app/serializers/pipeline_serializer.rb

@@ -24,6 +24,7 @@ class PipelineSerializer < BaseSerializer
   end
 
   def represent_status(resource)
+    return {} unless resource.present?
     data = represent(resource, { only: [{ details: [:status] }] })
     data.dig(:details, :status) || {}
   end