The IsMissing function may not work correctly when you declare a function with a parameter that is both optional and of the Variant data type in Visual Basic 6.0 (891406)

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Private Function SampleFunction(Optional f As Variant)
	On Error Resume Next
	If IsMissing(f) Then
		MsgBox ("Not Missing f")
	Else
		MsgBox ("Missing f")
	End If
End Function

Note This problem does not occur in versions of Microsoft Visual Basic that were released after Microsoft Visual Basic 6.0.