Add a report to spreeCommerce Admin

Question

What is the recommended way to add a report to Spree's admin area?

I can see the controller that adds them here:

https://github.com/spree/spree_backend/blob/main/app/controllers/spree/admin/reports_controller.rb

but doing this:

# /config/initializers/spree.rb
Spree::Admin::ReportsController.add_available_report!(:custom_report)

Gives error :

uninitialized constant Spree::Admin::ReportsController