Set based on expiration time is not present

Im trying to create a set that will include a date fields that i would like to check if one is not present. Obviously this can't be done through adding statements due to the lack of "is present"  & "is not present".  Would be nice to have considering the sync manager has these.  I know the below filter is for expirationtime is present...but that doesn't work either.

I received an error when trying to add this to the filter:

<Filter xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Dialect="http://schemas.microsoft.com/2006/11/XPathFilterDialect" xmlns="http://schemas.xmlsoap.org/ws/2004/09/enumeration">/Person[(EmployeeType = 'Employee') and (EmergencyTerm = False) and (EmployeeEndDate &lt; fn:current-dateTime()) and (ExpirationTime,'%')]</Filter>

Thoughts?