How do I define a Nullable DateTime variable in Visual COBOL ?

The DateTime fields I am inserting into my database can sometimes be null.  I want such fields in the table to show as null, not as "0001-01-01 12:00 AM".  You do this In C# by using DateTime? as your data type.  How do you do this in Visual COBOL ?  I haven't been able to find any documentation on it.