public static void merge(RoutingContext ctx) {
        merge(ctx, new HashSet<>(0));
    }
This is a convenient entry to the {@link #merge(RoutingContext,Set)} method by way of a routing context object.
The replies of all child contexts are merged and stored in the context.

@param ctx the context whose children to merge
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/DocumentProtocol.java