c# - 理解できないエラーが発生します。オブジェクト参照がオブジェクト インスタンスに設定されていません。どこで私は間違えましたか？

Question

144行目の私のコードは次のとおりです

peopleEntering.Add(new PersonEntered(personName, dateEntered, doorTypeEnum));

エラーが発生する場所です：オブジェクト参照がオブジェクトのインスタンスに設定されていません。なぜ？

  protected void btnUpload_Click(object sender, EventArgs e)
    {
        if (FileUpload1.PostedFile.FileName == string.Empty)
        {

            return;
        }
        else
        {
            string[] FileExt = FileUpload1.FileName.Split('.');
            string FileEx = FileExt[FileExt.Length - 1];
            if (FileEx.ToLower() == "csv")
            {
                FileUpload1.SaveAs(Server.MapPath(" " + FileUpload1.FileName));
            }
            else
            {

                return;
            }
        }
        CSVReader reader = new CSVReader(FileUpload1.PostedFile.InputStream);
        string[] headers = reader.GetCSVLine();
        DataTable dt = new DataTable();

        foreach (string strHeader in headers)
            dt.Columns.Add(strHeader);
        string[] data;
        while ((data = reader.GetCSVLine()) != null)
            dt.Rows.Add(data);
        foreach (DataRow row in dt.Rows)
        {
            string dateAndTime = row["Date and Time"].ToString();
            string personName = row["Description #2"].ToString();
            string doorType = row["Card number"].ToString();

            DateTime dateEntered = Convert.ToDateTime(dateAndTime);
            DoorType doorTypeEnum;

            bool personExists = false;
            foreach (object name in listboxOfNames.Items)
            {
                if (name.ToString() == personName)
                {
                    personExists = true;
                    break;
                }
            }
            if (!personExists)
            {
                listboxOfNames.Items.Add(personName);

            }
            switch (doorType)
            {
                case "A02 - Rear Entrance":
                    doorTypeEnum = DoorType.RearEntranceDoor;
                    break;
                case "B12 - Exterior Main Floor Man Trap":
                    doorTypeEnum = DoorType.ExteriorMainFloorDoor;
                    break;
                case "B12 - Interior Main Floor Man Trap":
                    doorTypeEnum = DoorType.InteriorMainFloorDoor;
                    break;
                case "C13 - Rear Break Room Door":
                    doorTypeEnum = DoorType.RearBreakRoomDoor;
                    break;
                case "B02 - Exterior Basement Man Trap":
                    doorTypeEnum = DoorType.ExteriorBasementDoor;
                    break;
                case "B02 - Interior Basement Man Trap":
                    doorTypeEnum = DoorType.InteriorBasementDoor;
                    break;
                case "D01 - Managed Services Main door":
                    doorTypeEnum = DoorType.ManagedServicesDoor;
                    break;
                case "D01 - Managed Services Big Door":
                    doorTypeEnum = DoorType.ManagedServicesBigDoor;
                    break;
                default:
                    doorTypeEnum = DoorType.None;
                    break;
            }
            peopleEntering.Add(new PersonEntered(personName, dateEntered, doorTypeEnum));
        }


        for (int i = 0; i < peopleEntering.Count; i++)
        {
            DateTime startDate = new DateTime();
            DateTime endDate = new DateTime();
            string personName = peopleEntering[i].PersonName;
            if ( peopleEntering[i].DoorEntered == DoorType.RearEntranceDoor)
            {
                startDate = peopleEntering[i].DateOfEntry;
                for ( int j = i + 1; j < peopleEntering.Count; j++)
                {
                    if (peopleEntering[j].DoorEntered == DoorType.ExteriorBasementDoor && peopleEntering[j].PersonName == personName)
                    {
                        endDate = peopleEntering[j].DateOfEntry;
                    }
                }

            }
            workSpans.Add(new WorkSpan(personName, startDate, endDate));

        }

        csvReaderGv.DataSource = dt.Rows;
        csvReaderGv.DataBind();
    }




            }