Introduce "zero priced orders" in admin order payments UI and helper

app/helpers/spree/payment_methods_helper.rb

@@ -4,12 +4,13 @@ module Spree
   module PaymentMethodsHelper
     def payment_method(payment)
       # hack to allow us to retrieve the name of a "deleted" payment method
-      id = payment.payment_method_id
+      return unless (id = payment.payment_method_id)
+
       Spree::PaymentMethod.find_with_destroyed(id)
     end
 
     def payment_method_name(payment)
-      payment_method(payment).name
+      payment_method(payment)&.name
     end
   end
 end

app/views/spree/admin/payments/_list.html.haml

@@ -11,7 +11,9 @@
       %tr{class: "#{cycle('odd', 'even')}"}
         %td= pretty_time(payment.created_at)
         %td.align-center= payment.display_amount.to_html
-        %td.align-center= link_to payment_method_name(payment), spree.admin_order_payment_path(@order, payment)
+        %td.align-center
+          - if payment.payment_method_id
+            = link_to payment_method_name(payment), spree.admin_order_payment_path(@order, payment)
         %td.align-center
           %span{class: "state #{payment.state}"}= t(payment.state, scope: "spree.payment_states", default: payment.state.capitalize)
         %td.actions