If a program contain arrays which keys contain zero characters \0. For example, such arrays become available when you cast object to array when object is instance of a class from a namespace.

Sample code 1:
namespace aaa\aaa;
class cls {
private $field;
}
$a = new cls();
$a = (array)$a;
if ($a) {}

Sample code 2:
$a = ["aa\0aa\0aa" => 'value'];
if ($a) {}