public function delete_custom_taxonomy(){
    global $wpdb;

    //checking the nonce
    check_admin_referer('delete_custom_taxonomy_mf_custom_taxonomy');

    if( isset($_GET['custom_taxonomy_id']) ){
      $id = (int)$_GET['custom_taxonomy_id'];

      if( is_int($id) ){
        $sql = $wpdb->prepare( "DELETE FROM ".MF_TABLE_CUSTOM_TAXONOMY." WHERE id = %d",$id );
        $wpdb->query($sql);
        $this->mf_redirect(null,null,array('message' => 'success'));
      }
    }
  }