Can't acccess personnal library

You are using CI methods inside the library without instanciating the CI. Take a look here: https://codeigniter.com/user_guide/gener...ur-library

...I am reffering to the "$this->db..." part.

Thank you very much it works !
Here is my new library :

PHP Code:

<?php defined('BASEPATH') OR exit('No direct script access allowed');

class Cms {

         public function __construct()
        {
                // Assign the CodeIgniter super-object
                $this->CI =& get_instance();
        }

        public function getTags($pageName)
        {
            
            $query = $this->CI->db->get_where('cms', array('page_name' => $pageName), 1);

            foreach ($query->result_array() as $row)
            {
                    return $row;
            }
        }
}