c# - 尝试运行 Microsoft 示例程序 ContactManager 时出错

Question

当我尝试为 asp.net core 2.1 运行 Contact Manager 程序时，当程序尝试为数据库设置种子时，我收到 ArgumentNullException 错误。

System.AggregateException
  HResult=0x80131500
  Message=One or more errors occurred.
  Source=ContactManager
  StackTrace:
   at ContactManager.Program.Main(String[] args) in C:\Users\EphraimF\source\repos\CMfinal\Program.cs:line 41

Inner Exception 1:
ArgumentNullException: Value cannot be null.

The error in generated because a null is returned by `userManager.FindByIdAsync(uid)`.

该 repo 是 asp.net core 2.1 文档的一部分，可在此处找到：https ://docs.microsoft.com/en-us/aspnet/core/security/authorization/secure-data?view=aspnetcore-2.1