Handled missing Offer when reading

no-issue

When attempting to read a non-existent offer we were running into issues
with calling toJSON() on `null`. This updates the handling to explicitly
return null - so that the controller can correctly throw a NotFoundError

ghost/offers/lib/application/OfferRepository.js

@@ -134,6 +134,10 @@ class OfferRepository {
             withRelated: ['product']
         });
 
+        if (!model) {
+            return null;
+        }
+
         return this.mapToOffer(model, options);
     }
 

ghost/offers/lib/application/OffersAPI.js

@@ -27,6 +27,10 @@ class OffersAPI {
 
             const offer = await this.repository.getById(data.id, options);
 
+            if (!offer) {
+                return null;
+            }
+
             return OfferMapper.toDTO(offer);
         });
     }