public DocsumDefinition getDocsum(String summaryClass) {
        if (summaryClass == null || summaryClass.isEmpty())
            summaryClass = "default";
        DocsumDefinition ds = definitionsByName.get(summaryClass);
        if (ds == null)
            ds = definitionsByName.get("default");
        if (ds == null)
            throw new ConfigurationException("Fetched hit with summary class " + summaryClass +
                                             ", but this summary class is not in current summary config (" + this + ")" +
                                             " (that is, you asked for something unknown, and no default was found)");
        return ds;
    }
Returns the summary definition of the given name, or the default if not found.

@throws ConfigurationException if the requested summary class is not found and there is none called "default"
container-search/src/main/java/com/yahoo/prelude/fastsearch/DocsumDefinitionSet.java