C# DateTimePicker控件设置空时间

//在DateTime旁边添加一个清空按钮.

private void btnClearRegTime_Click(object sender, EventArgs e)
{
MessageBox.Show("Text:" + dtpRegTime.Text + "\nValue:" + dtpRegTime.Value.ToString());
dtpRegTime.CustomFormat = "   ";
MessageBox.Show("Text:" + dtpRegTime.Text + "\nValue:"+dtpRegTime.Value.ToString());
}

dtpRegTime.CustomFormat = " ";的作用是让dtp.Text为"" ,但dtp.value其实还是时间值。录入数据库的事后要使用dtp.text.