[php-src] Issue #8055: PHP 8.0 how to append strings to unknown SESSION variables in a clean concise way without Warnings

Issue: https://github.com/php/php-src/issues/8055 Author: MHCreations ### Description PHP version 8.0.15 I have empty error logs because I have notices turned off and I code to the best of my abilities and to best practise as far as practical. The following code: ```php <?php session_start(); $_SESSION['message'] .= "Sorry; That file or location can not be found."; ``` Resulted in this output: ``` PHP Warning: Undefined array key "message" in /index.php on line 29 ``` But I expected this output instead: ``` String is generated without error. ``` The issue is that $_SESSION is an imported value; I can't force set the value as if a local variable; for fear of overwriting data in the session. A workaround is ``` if(array_key_exists('message', $_SESSION)){ $_SESSION['message'] .= "Sorry; That file or location can not be found."; } else { $_SESSION['message'] = "Sorry; That file or location can not be found."; } ``` But look at that -- it's 5 extra lines and is a clear failure of DRY programming. With some shorthand encasing it can be reduced down to ``` $_SESSION['message'] = (array_key_exists('message', $_SESSION)?$_SESSION['message']:"") ."Sorry; That file or location can not be found."; ``` Which is verbose, hard to read but still on one line, the additional code doesn't DO anything. Apart from hiding the warning message. Obviously turning off warning messages is not a good idea, and I am left with many, many websites using many thousands of instances of $_SESSION data concatenation that now generate verbose and pointless errors; causing genuine errors harder to find. **So;** Can using the array key exist WARNING be relegated to Notice for when string concatenation occurs or for when acted on superglobals (such as $_SESSION) which come into the PHP scope as data from outside and thus can't be set within the script itself. Thank you.