return NS_ERROR_NULL_POINTER;  NS_PRECONDITION(aResult != nsnull, "null ptr"); if (! aResult)
InMemoryDataSource::ArcLabelsOut(nsIRDFResource* aSource, nsISimpleEnumerator** aResult){    NS_PRECONDITION(aSource != nsnull, "null ptr");    if (! aSource)        return NS_ERROR_NULL_POINTER;    NS_PRECONDITION(aResult != nsnull, "null ptr");    if (! aResult)        return NS_ERROR_NULL_POINTER;    NS_AUTOLOCK(mLock);    InMemoryArcsEnumeratorImpl* result =        new InMemoryArcsEnumeratorImpl(this, aSource, nsnull);    if (! result)        return NS_ERROR_OUT_OF_MEMORY;    NS_ADDREF(result);    *aResult = result;    return NS_OK;}