Is this '??' is a operator in php or what it's called? Also is it used for empty() or isset() check?

Question

$name = $username ?? '';

I don't know actually what is this ?? called?

Answer 1

?? is Null coalescing Let suppose

$x = expr1 ?? expr2

Returns the value of $x.The value of $x is expr1 if expr1 exists, and is not NULL. If expr1 does not exist, or is NULL, the value of $x is expr2.Null coalescing Introduced in PHP 7.

Other Examples

<?php
   // variable $user is the value of $_GET['user']
   // and 'anonymous' if it does not exist
   echo $user = $_GET["user"] ?? "anonymous";
   echo("<br>");
  
   // variable $color is "red" if $color does not exist or is null
   echo $color = $color ?? "red";
?>