code: public GroupOptions addSort(@Nullable Sort sort) {
  
  		if (sort == null) {
  			return this;
  		}
  
  		if (this.sort == null) {
  			this.sort = sort;
  		} else {
  			this.sort = this.sort.and(sort);
  		}
  
  		return this;
  	}
docs: Adds {@link Sort} to instruct how to sort elements within a single group.
  
  @param sort
  @return