Blank Date Option

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I have a Calander Select button, but on my Calender there is a [Blank Date]
Option , which is not working is there something i should add to this code
to get the Blank date option.
Below is the Code to [Blank Date] on Calender:

Private Sub cmdCancel_Click()
Dim nRtnValue As Integer, dtDefault As Date
If IsNull(Me.OpenArgs) = True Then
DoCmd.Close acForm, Me.Name
Else
nWeek = 1
If IsNull(Me.OpenArgs) = True Then
dtDefault = Now()
Else
dtDefault = CDate(Me.OpenArgs)
End If
cbMonths.value = Month(dtDefault)
tbMonth = Month(dtDefault)
[cbYears] = Year(dtDefault)
nRtnValue = funSetCalender(dtDefault)
lbMonthYear.Caption = Format(dtDefault, "Long Date")
'Format(dtDefault, "dd/mm/yyyy")
tbDate.value = Format(dtDefault, "dd/mm/yyyy")
tbDate.value = ""
Me.Visible = False
End If
End Sub
Thanks for any help