public DocsumDefinition effectiveDocsumDef() {
        if (effectiveDocsumDef == null) {
            if (docsumDefinitions == null) {
                throw new IllegalStateException("missing docsumDefinitions");
            }
            throw new IllegalStateException("docsumDefinition missing for summary=" + askForSummary);
        }
        return effectiveDocsumDef;
    }
resolve summary class to use when none provided
container-search/src/main/java/com/yahoo/prelude/fastsearch/PartialSummaryHandler.java