private boolean ensureKnownClass(String wantClass) {
        if (knownSummaryClasses.containsKey(wantClass))
            return true;
        if (isFieldListRequest(wantClass)) {
            var fieldSet = parseFieldList(wantClass);
            if (fieldSet.isEmpty())
                return false;
            knownSummaryClasses.put(wantClass, fieldSet);
            return true;
        }
        if (docsumDefinitions != null && docsumDefinitions.hasDocsum(wantClass)) {
            var docsumDef = docsumDefinitions.getDocsum(wantClass);
            var fields = docsumDef.fields().keySet();
            var fieldSet = Set.copyOf(fields);
            knownSummaryClasses.put(wantClass, fieldSet);
            return true;
        }
        return false;
    }
resolve summary class to use when none provided
container-search/src/main/java/com/yahoo/prelude/fastsearch/PartialSummaryHandler.java