ADO Locate fails on empty DateTime fields


I have a table with the fields "Name" and "Date" where date can have empty

Name (String) - Date (DateTime)
John - 01/01/2000
John - <Null>

ADOTable1.Locate('name;date', VarArrayOf(sName, dtDateTime), [])

When i use locate to search for sName = 'John' and dtDateTime value is null
or empty the locate always fails.
But when i locate the record with sName = 'John' and dtDateTime =
'01/01/2000' it finds the correct record.

How can i use locate to search for a record where the datetime field is

I am using Delphi 5 Enterprise and ADO to connect to MS-SQL Server 7.  I
have installed the update pack for D5 enterprise and also the patch that was
done by Mark Edington.

With Regards