Use the letter_branding logo if it exists otherwise fall back to the dvla_organisation logo.

app/celery/letters_pdf_tasks.py

@@ -52,11 +52,13 @@ from app.models import (
 def create_letters_pdf(self, notification_id):
     try:
         notification = get_notification_by_id(notification_id, _raise=True)
-
+        # We only need this while we are migrating to the new letter_branding model
+        letter_logo_file_name = notification.service.letter_branding.filename if notification.service.letter_branding\
+            else notification.service.dvla_organisation.filename
         pdf_data, billable_units = get_letters_pdf(
             notification.template,
             contact_block=notification.reply_to_text,
-            filename=notification.service.dvla_organisation.filename,
+            filename=letter_logo_file_name,
             values=notification.personalisation
         )
 

app/template/rest.py

@@ -274,13 +274,15 @@ def preview_letter_template_by_notification_id(service_id, notification_id, file
         }
 
         service = dao_fetch_service_by_id(service_id)
-
+        # We only need this while we are migrating to the new letter_branding model
+        letter_logo_filename = service.letter_branding.filename if service.letter_branding \
+            else service.dvla_organisation.filename
         data = {
             'letter_contact_block': notification.reply_to_text,
             'template': template_for_letter_print,
             'values': notification.personalisation,
             'date': notification.created_at.isoformat(),
-            'filename': service.dvla_organisation.filename,
+            'filename': letter_logo_filename,
         }
 
         url = '{}/preview.{}{}'.format(