protected function _createSlug()
    {
        //Regenerate the slug
        if($this->isModified('slug')) {
            $this->slug = $this->_createFilter()->sanitize($this->slug);
        }

        //Handle empty slug
        if(empty($this->slug))
        {
            $slugs = array();
            foreach($this->_columns as $column) {
                $slugs[] = $this->_createFilter()->sanitize($this->$column);
            }

            $this->slug = implode($this->_separator, array_filter($slugs));
        }

        //Canonicalize the slug
        if($this->_unique) {
            $this->_canonicalizeSlug();
        }
    }