private void lessChildren() throws IOException {
        int lastRenderedChildren = renderedChildren.pop();
        if (lastRenderedChildren > 0) {
            generator.writeEndArray();
        }
    }
Creates a json renderer using a custom executor.
Using a custom executor is useful for tests to avoid creating new threads for each renderer registry.
container-search/src/main/java/com/yahoo/search/rendering/JsonRenderer.java