System.NullReferenceException: 未将对象引用设置到对象的实例

代码如下:
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;public partial class AddSpots : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            Label1.Text = "请添加景点信息！";
        }    }
    protected void TextBox2_TextChanged(object sender, EventArgs e)
    {    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string[] spotsurl = new string[5];
        if (FileUpload1.PostedFile.FileName == "" || FileUpload2.PostedFile.FileName == "" || FileUpload3.PostedFile.FileName == "" || FileUpload4.PostedFile.FileName == "" || FileUpload5.PostedFile.FileName == "")
        {
            this.Label1.Text = "请至少选择一个选择上传景点图片的地址！";
        }
        else
        {
            HttpFileCollection myfiles = Request.Files;
            for (int i = 0; i < myfiles.Count; i++)
            {
                HttpPostedFile mypost = myfiles[i];
                try
                {
                    if (mypost.ContentLength > 0)
                    {
                        string uploadName = mypost.FileName;
                        int idx = uploadName.LastIndexOf(".");
                        string suffix = uploadName.Substring(idx);
                        string pictureName = DateTime.Now.Ticks.ToString() + i.ToString() + suffix;//把参数i加上去 防止同一时间内图片重复,因为上传的是多幅图片.
                        string serverpath = Server.MapPath("~/uploadfile1/") + pictureName;
                        mypost.SaveAs(serverpath);
                        spotsurl[i] = "uploadfile1/" + pictureName;
                    }
                }
                catch (Exception ex)
                {
                    this.Label1.Text = "上传发生错误！原因：" + ex.Message.ToString();                }                string selectedarea = this.DropDownList1.SelectedItem.Value;
                SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
                conn.Open();
                SqlCommand Mycmd = new SqlCommand("insert into Scenic-Spots(name,discribe,imgurl1,imgurl2,imgurl3,imgurl4,imgurl5,area) values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + spotsurl[0].ToString() + "','" + spotsurl[1].ToString() + "','" + spotsurl[2].ToString() + "','" + spotsurl[3].ToString() + "','" + spotsurl[4].ToString() + "','" + selectedarea.ToString() + "')", conn);
                Mycmd.ExecuteNonQuery();
                conn.Close();
            }
        }
        this.Label1.Text = spotsurl[0].ToString();    }
}错误如下:
异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。源错误: 
行 60:                 SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
行 61:                 conn.Open();
行 62:                 SqlCommand Mycmd = new SqlCommand("insert into Scenic-Spots(name,discribe,imgurl1,imgurl2,imgurl3,imgurl4,imgurl5,area) values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + spotsurl[0].ToString() + "','" + spotsurl[1].ToString() + "','" + spotsurl[2].ToString() + "','" + spotsurl[3].ToString() + "','" + spotsurl[4].ToString() + "','" + selectedarea.ToString() + "')", conn);
行 63:                 Mycmd.ExecuteNonQuery();行 64:                 conn.Close();
我也百度了好长时间,刚开始学ASP.NET,搜不出来才上来问的,麻烦大家了!
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