Я получаю ошибку, так как ссылка на объект не установлена на объект in VB.NET когда я пытаюсь создать форму входа и регистрации в visual studio, подключившись

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вот код

Imports System.Data.SqlClient
Imports System.IO
Imports System.Exception
Imports System.SystemException
Imports System.NullReferenceException
Public Class signupform

    Private Property reader As SqlDataReader

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim TypeUser As String


        Dim level As Integer
        TypeUser = ComboBox2.Text
        If TypeUser = "adminstrator" Then
            level = 1
        ElseIf TypeUser = "users" Then
            level = 2
        ElseIf TypeUser = "others" Then
            level = 3
        End If
        Dim sql As String = "insert into employeeinfo(email,password,level)values('" & TextBox1.Text & "',convert(NVARCHAR(32),HashBytes('SHA1','" & TextBox2.Text & "'),2)," & level & ")"
        Signup(sql)
        MsgBox("signup success!")
    End Sub
    Private Sub Signup(ByVal sql As String)
        Dim cmd As New SqlCommand
        Try
            connection.Open()
            cmd.Connection = connection
            reader = cmd.ExecuteReader()
            cmd.CommandType = CommandType.Text
            cmd.CommandText = sql
            cmd.ExecuteNonQuery()
            cmd.Dispose()
            connection.Close()
        Catch ex As Exception
            MsgBox("Failed" & ex.ToString)

        End Try
    End Sub
    Private Sub signupform_load(sender As Object, e As EventArgs) Handles MyBase.Load
        ComboBox2.Text = "1"
    End Sub



End Class

Что я уже пробовал:

создание формы входа и регистрации

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