How Do You Add a Null in a DateTime Field?

Good morning everybody.

I'm trying to add a null into a SQL Server DateTime column called ShippedDate. With the below code I get an error message that says "Nullable object must have a value". This is driving me crazy. How do I do this?

Code:

---

    private void InsertHeader(Guid inG)
    {
        DateTime now = DateTime.Now;

        string po = txtPoNumber.Text;
        string cn = ddlCustomer.Text;
        DateTime? shippeddate = null;
        OrderHeaderBll.Insert(inG, now, calStartDate.SelectedDate, po, cn, shippeddate.Value);
    }

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Never mind guys. I found the solution. Thanks for looking.

cmd.Parameters.AddWithValue("@ShippedDate", DBNull.Value);