Bug : mysql_to_unix (PHP 7.4) and solution

Hi!
I'm upgrading from CI 3.1.10 to 3.1.13 and from PHP 5.6 to 7.4
In future I will upgrade to CI 4 and PHP 8, but now this is faster and seems to be workng very well.
But: mysql_to_unix in PHP 5.6 if I use : 
2022-01-01 -> works as expected.
PHP 7.4 return nothing.
The solution is this:
From this original function in CI 3.1.13:

PHP Code:

function mysql_to_unix($time = '')
 {
 // We'll remove certain characters for backward compatibility
 // since the formatting changed with MySQL 4.1
 // YYYY-MM-DD HH:MM:SS

 $time = str_replace(array('-', ':', ' '), '', $time);

 // YYYYMMDDHHMMSS
 return mktime(
 substr($time, 8, 2),
 substr($time, 10, 2),
 substr($time, 12, 2),
 substr($time, 4, 2),
 substr($time, 6, 2),
 substr($time, 0, 4)
 );
 } 


To this one with NULL added, because if you do not have all parameters, substr() will return false in some args, but only NULL seems to be acceptable.

PHP Code:

return mktime(
 substr($time, 8, 2)?:null,
 substr($time, 10, 2)?:null,
 substr($time, 12, 2)?:null,
 substr($time, 4, 2)?:null,
 substr($time, 6, 2)?:null,
 substr($time, 0, 4)?:null
 );