if (!aDataSource || !aResource || !aType) return NS_ERROR_NULL_POINTER;
RDFContainerUtilsImpl::IsA(nsIRDFDataSource* aDataSource, nsIRDFResource* aResource, nsIRDFResource* aType){    nsresult rv;    PRBool result;    rv = aDataSource->HasAssertion(aResource, kRDF_instanceOf, aType, PR_TRUE, &result);    if (NS_FAILED(rv)) return PR_FALSE;    return result;}