Why does it report an error when judging USER_ID after initialization?

Question

Answer 1

I feel there are 2 errors. I don’t know if they are correct or not. Please refer to them.

Error 1 The parent class is not initialized during initialization parnet::_initialize()

Error 2 empty and is_null are two concepts. Can an empty data be converted into flase? One is a null value

Answer 2

The usage is wrong

<?php
define("GREETING","Hello world!",TRUE);
echo constant("greeting");
?>

Replace line 17 with it, try

if(empty(constant('USER_ID')))