private function Testfunktion (byval Wert1 as string, optional byval _
  Standardwert as list(of string)=nothing) as list(of string)
 
if wert = 1 then
Testfunktion.add ("sdjh")
Testfunktion.add("iourh")
else
Testfunktion=Standardwert
endif
 
end function

dim Antwort as new List(Of string)=Testfunktion("1", "leer")