message: Add comment about why we have to narrow to Model
diff: @@ -28,6 +28,7 @@ export default class ApplicationSerializer extends JSONAPISerializer {
  if (this.request.queryParams.related_counts) {
  relatedCounts = this.request.queryParams.related_counts.split(',');
  }
  + // We have to narrow model here because keys in ModelInstanceShared don't have .models
  const related = (model as Model<T>)[relationship];
  const count = Array.isArray(related.models) ? related.models.length : 0;
  return relatedCounts.includes(this.keyForRelationship(relationship)) ? { count } : {};
  