if (inst == NULL)
if (inst == nsnull)
static nsresult nsVertScrollbarConstructor (nsISupports *aOuter, REFNSIID aIID, void **aResult){  nsresult rv;  nsISupports *inst = nsnull;  if ( NULL == aResult )  {    rv = NS_ERROR_NULL_POINTER;    return rv;  }  *aResult = NULL;  if (NULL != aOuter)  {    rv = NS_ERROR_NO_AGGREGATION;    return rv;  }    inst = (nsISupports *)(nsBaseWidget *)(nsWidget *)new nsScrollbar(PR_TRUE);  if (inst == NULL)  {    return NS_ERROR_OUT_OF_MEMORY;  }  NS_ADDREF(inst);  rv = inst->QueryInterface(aIID, aResult);  NS_RELEASE(inst);  return rv;}