Filling A Null Date Field

So I went searching through the forums and found a thread that provided coding for getting the # of years and months from two dates:

Function fAgeYM(StartDate As Date, EndDate As Date) As String
'Purpose: Returns the difference between StartDate and Date in full years and months
'To call:
' ? fAgeYM(#1/21/04#, #1/19/06#)
'Returns:
' 1 years 11 months

Dim intHold As Integer


intHold = Int(DateDiff("m", StartDate, EndDate)) + _
(EndDate < DateSerial(Year(EndDate), Month(EndDate), Day(StartDate)))

fAgeYM = Int(intHold / 12) & " years " & intHold Mod 12 & " months "

End Function
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That's perfect for what I'm wanting but I'm doing it with Hire/Term dates. So I want to be able to see how long past and present employees have worked in the company. Obviously that makes the Term field Null at times. With the coding above it requires a date to be in the EndDate field. How can I change it to allow for a null field in which the field would essentially be the current day's date? [Now()]