if (aPresShell == nsnull) {
if (!aPresShell) {
nsresult DocumentViewerImpl::GetDocumentSelection(nsISelection **aSelection, nsIPresShell * aPresShell){  if (aPresShell == nsnull) {    if (!mPresShell) {      return NS_ERROR_NOT_INITIALIZED;    }    aPresShell = mPresShell;  }  if (!aSelection) return NS_ERROR_NULL_POINTER;  if (!aPresShell) return NS_ERROR_NULL_POINTER;  nsCOMPtr<nsISelectionController> selcon;  selcon = do_QueryInterface(aPresShell);  if (selcon)     return selcon->GetSelection(nsISelectionController::SELECTION_NORMAL, aSelection);    return NS_ERROR_FAILURE;}