通过创建datetime传递null到sql server 2012 datetime的问题?变量到我的存储过程

这是我的业务对象层

public class Servicetransactionbol
{
    public Servicetransactionbol()
    {
        st_id = default(int);
        st_startdate = default(DateTime);
        st_enddate = default(DateTime);
    }
       private int st_id;
    private DateTime st_startdate;
    private DateTime st_enddate;
     public int STid
    {
        get { return this.st_id; }
        set { this.st_id = value; }
    }
    public DateTime STstartdate
    {
        get { return this.st_startdate; }
        set { this.st_startdate = value; }
    }
    public DateTime STenddate
    {
        get { return this.st_enddate; }
        set { this.st_enddate = value; }
    }
}

这是我的业务访问层

public class servicetransactionbal
{
    servicetransactiondal servicetransactionDAL = new servicetransactiondal();
    public void insertTransaction(Servicetransactionbol servicetransactionBOL)
    {
        try
        {
            servicetransactionDAL.Inserttransaction(servicetransactionBOL);
        }
        catch(Exception ex)
        {
            throw ex;
        }
        finally
        {
        }
    }
}

这是我的数据访问层

public class servicetransactiondal
{
   public void Inserttransaction(Servicetransactionbol servicetransactionBOL)
   {
       try
       {
           Database db = DatabaseFactory.CreateDatabase("GeniusStockTraders");
           DbCommand dbc = db.GetStoredProcCommand("Sproc_service_transaction");              
           db.AddOutParameter(dbc, "srvid", DbType.Int32, servicetransactionBOL.STid);
           db.AddInParameter(dbc, "srv_startdate", DbType.DateTime, servicetransactionBOL.STstartdate);
           db.AddInParameter(dbc, "srv_enddate", DbType.DateTime, servicetransactionBOL.STenddate);
           db.AddInParameter(dbc, "ttype", DbType.String, "insert_transaction");
           db.ExecuteNonQuery(dbc);
           dbc.Dispose();
       }
       catch (Exception ex)
       {
           throw ex;
       }
       finally
       {
       }
   }
 }

最后这是我在

后面的代码

    SqlDateTime? enddate;
    protected void btn_Save_Click(object sender, EventArgs e)
    {
        try
        {
            Database db = DatabaseFactory.CreateDatabase("GeniusStockTraders");
            servicetransactionBOL.STid = default(int);
            servicetransactionBOL.STscript = txt_script.Text;
            servicetransactionBOL.STstartdate = Convert.ToDateTime(txt_startdate.Text);
            if (string.IsNullOrEmpty(txt_enddate.Text))
            {
                enddate = SqlDateTime.Null;
                servicetransactionBOL.STenddate = (DateTime)enddate;
            }
            else
            {
                servicetransactionBOL.STenddate = Convert.ToDateTime(txt_enddate.Text);
            }

有了这个代码，我能够插入datetime的最小值，当我的文本字段为空，但我想插入NULL，当我的文本字段为空。我试过把datetime改成datetime?在我的业务对象层，然后我能够插入NULL值到我的enddate在LOCALHOST，但当我上传相同的文件在线它抛出一个异常

方法未找到:'System. 'datetime GeniusstocktradersBOL.ServeicetransactionBOL.get_STenddate () .

请帮我解决这个问题。

谢谢

DateTime? someValue = ... // could be null
db.AddInParameter(dbc, "some_name", DbType.DateTime,
    (object)someValue ?? DBNull.Value);