if (nsnull!=aValue) {
if (aValue) {
nsHTMLTableElement::SetTHead(nsIDOMHTMLTableSectionElement* aValue){  nsresult rv = DeleteTHead();  if (NS_FAILED(rv)) {    return rv;  }  if (nsnull!=aValue) {    nsCOMPtr<nsIDOMNode> child;    rv = GetFirstChild(getter_AddRefs(child));    if (NS_FAILED(rv)) {      return rv;    }         nsCOMPtr<nsIDOMNode> resultChild;    rv = InsertBefore(aValue, child, getter_AddRefs(resultChild));  }  return rv;}