如何将datetimepicker默认设置为空？

在Load中，初始化
this.dateTimePicker1.Format=DateTimePickerFormat.Custom;
his.dateTimePicker1.CustomFormat=" ";
在事件里写：

private void dateTimePicker1_ValueChanged(object sender, System.EventArgs e)
{
//this.dateTimePicker1.Format=DateTimePickerFormat.Long;
this.dateTimePicker1.CustomFormat=null;

}
这样就实现了，在程序初始化时dateTimePicker显示为空