Warning: Trying to access array offset on value of type null and SyntaxError: JSON.parse

[cimt]

evolution CE 1.4.20 clean install

PHP 7.4 works
PHP 8.0 dosnt work

Warning: Trying to access array offset on value of type null in ...\assets\plugins\multifields\base\Core.php on line 90

After clicking to select an element I get an error in the Browser Console:
Uncaught SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
onreadystatechange .../assets/cache/multifields/multifields.scripts.min.js?time=1658037565:1
getAction .../assets/cache/multifields/multifields.scripts.min.js?time=1658037565:1
getTemplate .../assets/cache/multifields/multifields.scripts.min.js?time=1658037565:1
setTemplate .../assets/cache/multifields/multifields.scripts.min.js?time=1658037565:1
onclick .../manager/?a=27&r=1&id=33:1