Add guard clause to ensure incoming params

When diff_note_id is missing, exit early instead of attempting to search
with a nil or empty string, which will raise an
ActiveRecord::RecordNotFound exception.

Changelog: fixed

app/workers/create_note_diff_file_worker.rb

@@ -10,6 +10,8 @@ class CreateNoteDiffFileWorker # rubocop:disable Scalability/IdempotentWorker
   feature_category :code_review
 
   def perform(diff_note_id)
+    return unless diff_note_id.present?
+
     diff_note = DiffNote.find_by_id(diff_note_id) # rubocop: disable CodeReuse/ActiveRecord
 
     diff_note&.create_diff_file

spec/workers/create_note_diff_file_worker_spec.rb

@@ -23,5 +23,14 @@ RSpec.describe CreateNoteDiffFileWorker do
         described_class.new.perform(non_existing_record_id)
       end
     end
+
+    context "when called with a missing diff_note id" do
+      it "returns nil without creating diff file" do
+        expect_any_instance_of(DiffNote).not_to receive(:create_diff_file)
+        .and_call_original
+
+        described_class.new.perform(nil)
+      end
+    end
   end
 end