Description:
------------
Version: 7.4.15-5+deb11u1

When you explode a string into an array, elements that contain nothing (null) are detectable as such via is_null.
The only way to tell is any array element doesn't contain a value is to
strlen(trim($a_array[2])) == 0, which gives you the result you want, but is a tad tedious. 
I'm sure in prior versions is_null($a_array[2] would return true when that array element is empty.
I cannot prove or disprove this as I don't have access to an older version of PHP.

Test script:
---------------
<?php

$a_string = "awsed|34r5|||gh||";
$a_array  = explode ("|", $a_string);
if (is_array($a_array)) {
	$a_count = count($a_array);
	echo "Number of Elements " . $a_count . PHP_EOL;
	for ($i = 0; $i < $a_count; $i++) {
		if (is_null($a_array[$i])) {
			echo "Element " . $i . " Is NULL" . PHP_EOL;
		} else {
			echo "Element " . $i . " is " . $a_array[$i] . PHP_EOL;
		}
	}
} else {
	echo "NOT AN ARRAY" . PHP_EOL;
}
?>




Expected result:
----------------
Number of Elements 7
Element 0 is awsed
Element 1 is 34r5
Element 2 Is NULL 
Element 3 Is NULL
Element 4 is gh
Element 5 Is NULL
Element 6 Is NULL

Actual result:
--------------
Number of Elements 7
Element 0 is awsed
Element 1 is 34r5
Element 2 is 
Element 3 is 
Element 4 is gh
Element 5 is 
Element 6 is