PHP – Unidentified index in error log even though using isset to check for session variable

I am running the following check in PHP (in a Slim middleware) to make sure that a certain session variable exists:

public function __invoke($request, $response, $next) {

    if (isset($_SESSION['errors'])) { // this is line 17
      // do something
    }

    $response = $next($request, $response);
    return $response;

}

However, my error log is swamped with the following:

PHP Notice:  Undefined index: errors in /our/path/app/Middleware/ValidationErrorsMiddleware.php on line 17

What can I do to have this not show as an error?

I found a solution here: PHP: Notice Undefined index even using isset but my case is different as I’m not accessing the variable prior to the check.

Answer

You can use array_key_exists instead of isset

if(array_key_exists('errors', $_SESSION)) {
 //Do something
}

Here you can find the docs: https://www.php.net/manual/es/function.array-key-exists.php