@Override
    public void freeze() {
        if (isFrozen()) return;
        for (PageElement element : renderers) {
            if (element instanceof Renderer) {
                assignRendererForIfNotSet((Renderer)element);
            }
            else if (element instanceof Choice) {
                for (List<PageElement> renderersAlternative : ((Choice)element).alternatives()) {
                    for (PageElement rendererElement : renderersAlternative) {
                        Renderer renderer=(Renderer)rendererElement;
                        if (renderer.getRendererFor()==null)
                            renderer.setRendererFor(name);
                    }
                }
            }
            element.freeze();
        }
        parameters = Collections.unmodifiableMap(parameters);
        hashCode=hashCode();
        super.freeze();
    }
Returns the parameters of this source as a live reference (never null).
The parameters will be passed to the provider getting source data.
container-search/src/main/java/com/yahoo/search/pagetemplates/model/Source.java