@Override
    public void set(CompoundName key, Object obj, Map<String,String> context) {
        if(key == null) return;
        parent.set(getPathPrefix() + "." + key, obj, context);
    }
A wrapper around a chain of property objects that prefixes all gets/sets with a given path

@author Arne Bergene Fossaa
@deprecated Unused and will go away on vespa 9
container-search/src/main/java/com/yahoo/search/query/properties/SubProperties.java