When I tried to get this website working, the server running PHP5.4 threw me this error: Can't use method return value in write context.

Then, I found this StackOverflow comment from Kornel...

He stated that:

However, the real problem you have is that you use empty() at all, mistakenly believing that "empty" value is any different from "false".

Empty is just an alias for !isset($thing) || !$thing. When the thing you're checking always exists, the empty() function is nothing but a negation operator.

Here is a small benchmark I made to demonstrate it:

<?php
/*
 * Testing empty() VS negation '!'
*/

// Array of value
$var = [null, true, false, 0, 1, '0', '1', ''];
foreach ($var as $v) {
  debug([empty($v), !$v]);
}


/*
 * Outputs
*/

//null
[
	(int) 0 => true,
	(int) 1 => true
]

// true
[  
	(int) 0 => false,
	(int) 1 => false
]

// false
[  
	(int) 0 => true,
	(int) 1 => true
]

// 0 
[
	(int) 0 => true,
	(int) 1 => true
]

// 1
[
	(int) 0 => false,
	(int) 1 => false
]

// '0'
[
	(int) 0 => true,
	(int) 1 => true
]

// '1'
[
	(int) 0 => false,
	(int) 1 => false
]

// ''
[
	(int) 0 => true,
	(int) 1 => true
]