C＃Null引用异常，Object引用未设置为对象的实例

Question

所以我试图连接到MySQL数据库来检索信息，但我得到了空引用异常..

这是我的代码：

logIn.cs

    using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using MySql.Data.MySqlClient;

namespace StoreInventory
{
    public partial class logIn : Form
    {

        public logIn()
        {
            InitializeComponent();
            dbObject mysqlcon = new dbObject();
            mysqlcon.connectToDb();
        }

        private void confirmButton_Click(object sender, EventArgs e)
        {
            dbObject db = new dbObject();
            MySqlConnection con;
            string username = userBox.Text;
            string password = pwBox.Text;
            string query = "SELECT * FROM `users` WHERE username='" + username + "' AND password='" + password + "'";

            con = new MySqlConnection(db.connection.ConnectionString);
            con.Open();

            MySqlDataReader reader = null;
            MySqlCommand cmd = new MySqlCommand(query, con);

            reader = cmd.ExecuteReader();

            while (reader.Read()) 
            {
                MessageBox.Show(reader.GetString(0));
            }




        }
    }
}

dbObject.cs

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;
using System.Windows.Forms;

namespace StoreInventory
{
    class dbObject
    {
        public MySqlConnection connection;
        private string server;
        private string database;
        private string username;
        private string pasword;

        public void connectToDb()
        {

            string server = "localhost";
            string database = "shopdb";
            string username = "root";
            string pasword = "";
            string connectionString;
            connectionString = "SERVER=" + server +";" + "DATABASE=" + 
            database + ";" + "UID=" + username + ";" + "PASSWORD=" + pasword + ";";
            try
            {
                connection = new MySqlConnection(connectionString);
                connection.Open();
            }
            catch (MySqlException err)
            {
                MessageBox.Show("Error: " + err, "Fatal error");

            }
            finally
            {
                if (connection != null)
                {
                    connection.Close();
                }
            }
        }





    }


}

我做错了什么？我花了半个小时试图解决它，但我无法找到它...抱歉，如果它是一个愚蠢的错误，我还是新的。

提前致谢。