Thanks very much for the tip, it helps!
On my side, i used it as following to put content is an excel sheet :
If IsEmpty(theBug.Field("BG_TARGET_RCYC")) Then ' Target Cycle (rempli manuellement dans le suivi)
objSheet.Cells(i, 16).Value = "RCYC = NULL"
Else
objSheet.Cells(i, 16).Value = theBug.Field("BG_TARGET_RCYC").Name
End If