code: public Ordering createNewOrderingUpToIndex(int exclusiveIndex) {
  		if (exclusiveIndex == 0) {
  			return null;
  		}
  		final Ordering newOrdering = new Ordering();
  		for (int i = 0; i < exclusiveIndex; i++) {
  			newOrdering.appendOrdering(this.indexes.get(i), this.types.get(i), this.orders.get(i));
  		}
  		return newOrdering;
  	}
docs: Creates a new ordering the represents an ordering on a prefix of the fields. If the
  exclusive index up to which to create the ordering is <code>0</code>, then there is
  no resulting ordering and this method return <code>null</code>.
  
  @param exclusiveIndex The index (exclusive) up to which to create the ordering.
  @return The new ordering on the prefix of the fields, or <code>null</code>, if the prefix is empty.