[php] PHP shorthand for isset()?

Is there a shorthand way to assign a variable to something if it doesn't exist in PHP?

if(!isset($var) {
  $var = "";
}

I'd like to do something like

$var = $var | "";

PHP 7.4+; with the null coalescing assignment operator

$var ??= '';

PHP 7.0+; with the null coalescing operator

$var = $var ?? '';

PHP 5.3+; with the ternary operator shorthand

isset($var) ?: $var = '';

Or for all/older versions with isset:

$var = isset($var) ? $var : '';

or

!isset($var) && $var = '';