关于.NET使用ODP特性导入Oracle数据库的时间类型问题

[Smile_Liber]

具体代码如下，问题也在代码里面，请大侠们帮帮忙，谢谢

//设置一个数据库的连接串 
string connectStr = "User Id=scott;Password=tiger;Data Source="; 
OracleConnection conn = new OracleConnection(connectStr); 
OracleCommand command = new OracleCommand(); 
command.Connection = conn; 
//这个参数需要指定每次批插入的记录数 
command.ArrayBindCount = recc; 

command.CommandText = "insert into dept values(:uid, :uname, :ubirthday)"; 
conn.Open(); 

int[] uid = new int[recc]; 
string[] uname = new string[recc]; 
DateTime[] ubirthday = new DateTime[recc]; 

OracleParameter deptUid = new OracleParameter("uid", OracleDbType.int32, uid, ParameterDirection.Input);
OracleParameter deptUname = new OracleParameter("uname", OracleDbType.Varchar2, uname, ParameterDirection.Input);
OracleParameter deptUbirthday = new OracleParameter("ubirthday", OracleDbType.Date, ubirthday, ParameterDirection.Input);
comm.Parameters.Add(deptUid);
comm.Parameters.Add(deptUname);
comm.Parameters.Add(deptUbirthday);
//计时器          
Stopwatch sw = new Stopwatch(); 
sw.Start(); 

for (int i = 0; i < recc; i++) 
{ 
uid[i] = i; 
uname[i] = i.ToString(); 
ubirthday[i] = 空时间（null）这里要如何设置导入到Oracle数据库中使日期型的为空值，我用Convert.ToDateTime(null)在数据库中显示的是最原始的时间，我想要让它显示空，请知道的朋友帮帮忙 ，谢谢
} 
command.ExecuteNonQuery(); 

sw.Stop(); 
System.Diagnostics.Debug.WriteLine("批量插入:" + recc.ToString() + "所占时间:" +sw.ElapsedMilliseconds.ToString());