PHP variables to be empty string or NULL in making a determination.

test_blank.php

<?php
// bad example
$v = '0';
if ( empty($v) ) {
    echo '$v is blank.';
}

// good example
$v = '0';
if ( strlen($v)==0 ) {
    echo '$v is blank.';
}

// or use is_blank function
function is_blank($str) {
    return strlen($v)===0;
}

if ( is_blank($v) ) {
    echo '$v is blank.'
}

// It is safer to write PHP code that you can type Even with awareness.