3v4l.org

run code in 200+ php & hhvm versions
Bugs & Features
<?php $a = '{"ServiceUserData":"{"id":166001,"id_esia":null,"email":"i.razdymaho@netrika.ru","fio":"\u0420\u0430\u0437\u0434\u044b\u043c\u0430\u0445\u043e \u0418\u0433\u043e\u0440\u044c \u0412\u043b\u0430\u0434\u0438\u043c\u0438\u0440\u043e\u0432\u0438\u0447","is_active":true,"is_blocked":false,"unlock_at":"01.01.1970","register_date":"01.01.1970"}","PetersburgeduAuthUserId":"166793","STID":"5bd9aa4f5354a321942982","last_active_time":1540991568}'; var_dump(json_decode($a, true));
based on sBZB7
Output for 5.6.38 - 7.3.0rc3
NULL