PHP 7添加了null coalesce operator：
// Fetches the value of $_GET['number'] and returns 'nonumber -NULL'
// if it does not exist.
$username = $_GET['number'] ?? 'No Number';
// This is equivalent to:
$username = isset($_GET['number']) ? $_GET['number'] : 'No Number';
还有空的东西吗？
寻找类似的东西，
/ Fetches the value of $_GET['number'] and returns '0' Empty
// if it does not empty.
$username = $_GET['number'] ?? 'no number or number is 0 or empty';