why php notice is not getting ignored?

by

Also in wp-config.php, set the WP_DEBUG_DISPLAY constant to FALSE.

Snippet from wp-includes/default-constants.php:

// Add define('WP_DEBUG_DISPLAY', null); to wp-config.php use the globally configured setting for
// display_errors and not force errors to be displayed. Use false to force display_errors off.
if ( !defined('WP_DEBUG_DISPLAY') )
    define( 'WP_DEBUG_DISPLAY', true );