Handle case of BackorderJob having no work

app/jobs/backorder_job.rb

@@ -40,6 +40,8 @@ class BackorderJob < ApplicationJob
     user = order.distributor.owner
     items = backorderable_items(order)
 
+    return if items.empty?
+
     # We are assuming that all variants are linked to the same wholesale
     # shop and its catalog:
     reference_link = items[0].variant.semantic_links[0].semantic_id

spec/jobs/backorder_job_spec.rb

@@ -104,6 +104,14 @@ RSpec.describe BackorderJob do
       # Clean up after ourselves:
       perform_enqueued_jobs(only: CompleteBackorderJob)
     end
+
+    it "succeeds when no work to be done" do
+      # The database can change before the job is run. So maybe there's nothing
+      # to do.
+      expect {
+        subject.place_backorder(order)
+      }.not_to raise_error
+    end
   end
 
   describe "#place_order" do