An API call using format=php does not work in 12.1.0.

/ws.php?method=pwg.categories.getImages&format=php&per_page=2&recursive=true&order=random%20DESC

Error:

Got error 'PHP message: PHP Fatal error:  Uncaught TypeError: get_class(): Argument #1 ($object) must be of type object, array given in /include/ws_protocols/php_encoder.php:13

Explictly converting to object fixes the problem temporarily.

13: $respClass = strtolower( @get_class((object) $response) );