public function getDimensionKeys()
    {
        $dimensions = Config::get('imageupload.dimensions');

        $fillable = [];

        if (empty($dimensions) || ! is_array($dimensions)) {
            return $fillable;
        }

        foreach ($dimensions as $name => $dimension) {
            foreach ($this->thumbnailKeys as $key => $cast) {
                array_push($fillable, $name.'_'.$key);
            }
        }

        return $fillable;
    }