I was practicing your article titled

Simple User Registration Form Example in ASP.Net

but then, after i finished and played the program, i received this error

Cannot insert the value NULL into column 'UserId', table 'practicewebsite.dbo.Users'; column does not allow nulls. INSERT fails. The statement has been terminated.

the line that produces this error is

userId = Convert.ToInt32(cmd.ExecuteScalar())

Please help, Any comments will be so much appreciated, thank you people! :-)