您收到错误消息是因为 Configuration.GetConnectionString（ MigrationConnection）返回 null 。应当替换为：

You're getting the error because Configuration.GetConnectionString("MigrationConnection") returns null. It should be replaced with:

var connection = Configuration.GetSection("Data").GetConnectionString("MigrationConnection");

或者您可以将appsettings.json的结构更改为：

Or you can change the structure of appsettings.json to:

{
    "ConnectionStrings": {
      "DefaultConnection": "server=database;userid=hawai;pwd=mysecret;port=3306;database=identity;sslmode=none;",
      "MigrationConnection": "server=127.0.0.1;userid=hawai;pwd=mysecret;port=3306;database=identity;sslmode=none;"
    }  
}