code: public SimpleConfiguration orElse(SimpleConfiguration fallback) {
      SimpleConfiguration copy = new SimpleConfiguration(this);
      for (Map.Entry<String, String> entry : fallback.toMap().entrySet()) {
        if (!copy.containsKey(entry.getKey())) {
          copy.setProperty(entry.getKey(), entry.getValue());
        }
      }
      return copy;
    }
docs: @param fallback SimpleConfiguration to join together
  @return a new simple configuration that contains all of the current properties from this plus
  the properties from fallback that are not present in this.
  
  @since 1.2.0