PHP Parse error: syntax error, unexpected '?' in /path/to/file.php

Symptoms

The following error is logged to your PHP-based website or application error log. The error may also be displayed when visiting the PHP-based website or application in a browser.

PHP Parse error: syntax error, unexpected '?' in /path/to/file.php on line $LineNumber

Description 

This typically occurs when the PHP-based website or application is using an older version of PHP and attempts to use the PHP null coalescing operator, "??".

Workaround

The null coalescing operator, "??", was introduced in PHP 7.0. Use PHP 7.0 or later for your website or application. Please see: How to change the PHP version for a domain in cPanel or WHM

More information on the null coalescing operator can be found in PHP documentation here:

php.net - Migrating from PHP 5.6.x to PHP 7.0.x - New Features