class ConfigurationUtils {

  public static void injectDefaults(Configuration source,
      Configuration target) {
    Check.notNull(source, "source");
    Check.notNull(target, "target");
    for (Map.Entry<String, String> entry : source) {
      if (target.get(entry.getKey()) == null) {
        target.set(entry.getKey(), entry.getValue());
      }
    }
  }

}