@Override
    public String toString() {
        if (isEmpty()) return "empty BCP";
        return "BCP of " +
               ( groups.isEmpty() ? "no groups" : groups ) +
               (defaultDeadline.isEmpty() ? "" : ", deadline: " + defaultDeadline.get());
    }
Returns this bcp spec, or if it is empty, the given bcp spec.
config-model-api/src/main/java/com/yahoo/config/application/api/Bcp.java