var entities: [Post] = []
    if startKey == nil {//nextToken == nil: no more posts
        return
    }
    let query = ListPostsQuery()
    query.limit = 2
    if startKey != "" {//when the app starts startKey == “”
        query.nextToken = startKey
    }

    appSyncClient?.fetch(query: query) {(result, error) in
      //code
    })