Method check

/**
 * Assert that the nested set data is valid.
 *
 * @return  boolean  True if the instance is sane and able to be stored in the database.
 *
 * @since   1.7.0
 */
public function check()
{
    try {
        parent::check();
    } catch (\Exception $e) {
        $this->setError($e->getMessage());
        return false;
    }
    $this->parent_id = (int) $this->parent_id;
    if (empty($this->rules)) {
        $this->rules = '{}';
    }
    // Nested does not allow parent_id = 0, override this.
    if ($this->parent_id > 0) {
        // Get the DatabaseQuery object
        $query = $this->_db->getQuery(true)->select('1')->from($this->_db->quoteName($this->_tbl))->where($this->_db->quoteName('id') . ' = ' . $this->parent_id);
        $query->setLimit(1);
        if ($this->_db->setQuery($query)->loadResult()) {
            return true;
        }
        $this->setError(Text::_('JLIB_DATABASE_ERROR_INVALID_PARENT_ID'));
        return false;
    }
    return true;
}