def invoiceLink(self,obj):
if hasattr(obj, '<STR_LIT>') and obj.invoiceItem:<EOL><INDENT>return self.get_admin_change_link('<STR_LIT>', '<STR_LIT>', obj.invoiceItem.invoice.id, _('<STR_LIT>'))<EOL><DEDENT>
If vouchers app is enabled and there is a voucher, this will link to it.