function process_filter_form_empty()
{
    $auction_set = array();
    $short = array('auctionId' => 2, "title" => "title", "description" => "description", "currentPrice" => 10, "stars" => 1, "category_id" => 5);
    $short_spaces = array('auctionId' => 3, "title" => "title with spaces", "description" => "description with spaces", "currentPrice" => 10, "stars" => 2, "category_id" => 5);
    $different = array('auctionId' => 4, "title" => "different", "description" => "same description", "currentPrice" => 10, "stars" => 3, "category_id" => 5);
    $costly = array('auctionId' => 5, "title" => "auction with long description", "description" => "very long description", "currentPrice" => 100, "stars" => 4, "category_id" => 5);
    $wrong_category = array('auctionId' => 5, "title" => "auction with long description", "description" => "very long description", "currentPrice" => 100, "stars" => 4, "category_id" => 1000);
    array_push($auction_set, $short, $short_spaces, $different, $costly);
    $result = process_filter_form($auction_set, 50, 200, 5, 5);
    assert(empty($result));
    echo "Auctions list after filtering: ";
    echo "<pre>";
    echo "Should print null just below: ";
    print_r($result);
    echo "<br/>Should print null just above: ";
    echo "</pre>";
}
             //enrich with price
             $current_price = get_price($auction_set[$i]['auctionId'], $auction_set[$i]['startingPrice']);
             $auction_set[$i]['currentPrice'] = $current_price;
             //once the current price is known, there is no further need for a
             //startingPrice field on the retrieved associative array
             unset($auction_set[$i]['startingPrice']);
             //enrich with rating
             $feedback_array = query_select_user_rating($auction_set[$i]['seller']);
             $auction_set[$i]['stars'] = $feedback_array['stars'];
             $auction_set[$i]['no_of_ratings'] = $feedback_array['occurrences'];
         }
     }
 } else {
     $auction_set = $_POST['auctionSet'];
 }
 $auction_set = process_filter_form($auction_set, $_POST['bottom'], $_POST['top'], $_POST['rating'], $_POST['category']);
 //begin constructing auction set display table, id value used by
 //jQuery to replace construct with ajax request response
 //begin constructing table
 $output = "\n              <table class=\"search-page-table table-striped\" id=\"results\">\n                  <col width=\"200px\">\n                  <col width=\"400px\">\n                  <col width=\"800px\">";
 //if (filtered if requested) result set is not empty:
 if ($auction_set) {
     foreach ($auction_set as $auction) {
         $imageName = htmlentities($auction['imageName']);
         $title = htmlentities($auction['title']);
         $auctionId = htmlentities($auction['auctionId']);
         $currentPrice = htmlentities($auction['currentPrice']);
         $description = htmlentities($auction['description']);
         $rating_string = "The seller has not yet been rated<br/>";
         if ($auction['no_of_ratings'] > 0) {
             $rating = htmlentities($auction['stars']);