public static void select(Selectable selectable, ObjectPredicate predicate, ObjectOperation operation) {
        if (selectable != null) {
            selectable.select(predicate, operation);
        }
    }
Invokes {@link #select(ObjectPredicate, ObjectOperation)} on any member objects this object wants to expose
through the selection mechanism. Overriding this method is optional, and which objects to expose is determined by
the application logic of the object itself.

@param predicate component used to select (sub-)objects
@param operation component performing some operation on the selected (sub-)objects
vespajlib/src/main/java/com/yahoo/vespa/objects/Selectable.java