Description:
------------
If we execute the function `exec` passing the `$result_code` but not passing the `$output`, it gives us a segfault error. This was discovered here:
https://github.com/cviniciussdias/php-text-to-speech/issues/2

And can be reproduced here:
https://3v4l.org/NeONG

Test script:
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<?php

echo 'Executing with all params:' . PHP_EOL;
exec('echo Something', output: $output, result_code: $resultCode);

echo 'Executing without output param:' . PHP_EOL;
exec('echo Something', result_code: $resultCode);

echo 'The End';

Expected result:
----------------
No errors should be displayed and the command should be executed.

Actual result:
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Process exited with code 139.