private Index getIndexFromDocumentTypes(String indexName, List<String> documentTypes) {
        if (indexName == null || indexName.isEmpty())
            indexName = "default";

        return getIndexByCanonicNameFromDocumentTypes(indexName, documentTypes);
    }
Whether this has (any) NGram indexes. Calculated at freeze time.
container-search/src/main/java/com/yahoo/prelude/IndexFacts.java