docs: public Ordering appendOrdering(Integer index, Class<? extends Comparable<?>> type, Order order) {
  		if (index < 0) {
  			throw new IllegalArgumentException("The key index must not be negative.");
  		}
  		if (order == null) {
  			throw new NullPointerException();
  		}
  		if (order == Order.NONE) {
  			throw new IllegalArgumentException("An ordering must not be created with a NONE order.");
  		}
  
  		if (!this.indexes.contains(index)) {
  			this.indexes = this.indexes.addField(index);
  			this.types.add(type);
  			this.orders.add(order);
  		}
  
  		return this;
  	}