code: public function add($key, $value)
      {
          if ($value === false) {
              return;
          }
          if (is_array($value)) {
              foreach ($value as $item) {
                  $this->addPair($key, $item);
              }
          } else {
              $this->addPair($key, $value);
          }
      }
docs: Adds a parameter to the query.
  
  @param string $key            Key to add value to.
  @param string/array $value    New data.