<?php
$test = array();
$test['eval_none'] = '';
$test['eval_zero'] = 0;
$test['eval_null'] = null;
$test['eval_false'] = false;
$test['eval_true'] = true;
if (isset($test['eval_none'])) var_dump('None is set.');
if (!empty($test['eval_none'])) var_dump('None is not empty.');
if (isset($test['eval_zero'])) var_dump('Zero is set.');
if (!empty($test['eval_zero'])) var_dump('Zero is not empty.');
if (isset($test['eval_null'])) var_dump('NULL is set.');
if (!empty($test['eval_null'])) var_dump('NULL is not empty.');
if (isset($test['eval_false'])) var_dump('False is set.');
if (!empty($test['eval_false'])) var_dump('False is not empty.');
if (isset($test['eval_true'])) var_dump('True is set.');
if (!empty($test['eval_true'])) var_dump('True is not empty.');
string(12) "None is set."
string(12) "Zero is set."
string(13) "False is set."
string(12) "True is set."
string(18) "True is not empty."
Output for 8.3.5
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
string(12) "None is set."
string(12) "Zero is set."
string(13) "False is set."
string(12) "True is set."
string(18) "True is not empty."