title: Function optional parameter DATE type Fails
body: <p>I have a function that finds the following Monday for a date. When no optional date parameter is passed it goes to a default of zero. I think I've included comments to explain problem</p>
  
  <pre><code>Function NextMondayFromADateOrToday(Optional StartDate As Date) As Date
  ' objective: if date param not supplied should set StartDate to today
  ' ??? Problem: with no arg provided StartDate is zero = date value of 1/1/1900
  ' ??? how to add default to optional paramater of date type?
  ' ??? or, how to check if an arg was provided if the parameter is date type?
  If Not (IsDate(StartDate)) Then StartDate = Date
  Select Case Weekday(StartDate)
  Case 1:     NextMondayFromADateOrToday = StartDate + 1
  Case 2:     NextMondayFromADateOrToday = StartDate + 0
  Case 3:     NextMondayFromADateOrToday = StartDate + 6
  Case 4:     NextMondayFromADateOrToday = StartDate + 5
  Case 5:     NextMondayFromADateOrToday = StartDate + 4
  Case 6:     NextMondayFromADateOrToday = StartDate + 3
  Case 7:     NextMondayFromADateOrToday = StartDate + 2
  End Select
  End Function
  </code></pre>