public function getSortURL($direction = false)
    {
        if (!$direction) {
            // No direction indicated, determine automatically from defaults.
            $direction = $this->getDirection();

            if ($this->isSorted()) {
                // If we are already sorting by this column, swap the direction
                $direction = $direction == 'asc' ? 'desc' : 'asc';
            }
        }

        // Generate and return a URL which may be used to sort this column
        return $this->generateUrl(array_filter([
            config('gbrock-tables.key_field')     => $this->getField(),
            config('gbrock-tables.key_direction') => $direction,
        ]));
    }