normalizeSingleResponse(store: DS.Store, primaryModelClass: DS.Model, payload: database.DataSnapshot, _id: string | number, _requestType: string) {
    if (!payload.exists) { throw  new DS.NotFoundError(); }
    let normalized = normalize(store, primaryModelClass, payload);
    this.applyTransforms(primaryModelClass, normalized.data.attributes);
    return normalized;