This sounds wrong. What changes have you done to your functions.php?

@mikaykun I pasted the code which is in the README.md but I got errors so I did some search and found that code I wrote to you and it worked for me. There is no need to update the README.md but put it in case someone like me needed.

Can you provide a example code so that we can fixed this issue or create a better solution for others and add it to the Readme. That would be nice.

I think@maheraldous is right. With

if ( !file_exists(get_template_directory() .'/class-wp-bootstrap-navwalker.php' ) ) {// File does not exist... return an error.returnnewWP_Error('class-wp-bootstrap-navwalker-missing',__('It appears the class-wp-bootstrap-navwalker.php file may be missing.','wp-bootstrap-navwalker' ) );}else {// File exists... require it.require_onceget_template_directory() .'/class-wp-bootstrap-navwalker.php';}

you simply return an instance of the WP_Error class holding the error codeclass-wp-bootstrap-navwalker-missing and the error messageIt appears the class-wp-bootstrap-navwalker.php file may be missing.. But the object is not processed in anyway, ie won't show up anywhere.

@maheraldous solution is a complicated way to echo the error message onevery page (admin and non-admin pages for logged in and logged out users).

My proposal is

$file =get_template_directory() .'/class-wp-bootstap-navwalker.php';if ( !file_exists($file ) ) {// Files does not exist, add admin notice.add_action('admin_notices',function() {$message =sprintf(/* translators: path to file */__('The file class-wp-bootstap-navwalker.php cannot be found at %s.','wp-bootstrap-navwalker' ),get_template_directory());printf('<div><p>%s</p></div>',esc_html($message ) );} );}else {// File exists, require it.require_once$file;}

which adds an admin notice on admin pages if the file does not exist.