Null reference exception was unhandled - ajuda

Imports System.Data.SqlClient

Imports MySql.Data.MySqlClient

Public Class LoginForm1

    Dim conexao As MySqlConnection

    Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click

        conexao = New MySqlConnection

        Dim servidor As String = "localhost"

        Dim usuario As String = "root"

        Dim senha As String = ""

        Dim banco As String = "usuario"

        conexao.ConnectionString = "server=" & servidor & ";user id=" & usuario & ";password=" & senha & "; database=" & banco & ";"

        conexao.Open()

        Dim adpt As New MySqlDataAdapter

        Dim verificar = "SELECT * FROM usuarios WHERE login = '" & txtusuario.Text & "' AND senha='" & txtsenha.Text & "'; "

        Dim comando As New MySqlCommand

        comando.Connection = conexao

        comando.CommandText = verificar

        adpt.SelectCommand = comando

        Dim database As MySqlDataReader

        database = comando.ExecuteReader

        If database.HasRows = 0 Then

            MsgBox("Erro ao efetuar login")

        Else

            Form1.Show()

            Me.Close()

        End If

    End Sub

 

    Private Sub Cancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Cancel.Click

        Me.Close()

    End Sub

 

End Class