PHP 5.6 Unexpected '?'

[imReallyUnoriginal]

Caused by #391, the syntax to have a nullable type using a question mark before it wasn't added until PHP 7.1, so AbstractProcessor throws an error on line 67

[TheDigitalOrchard]

PHP 5.6 is End-of-Life. Is there any particular reason that you're staying on that version and can't upgrade?

[imReallyUnoriginal]

I am working on a very large project with a lot of technical debt. We're in the process of moving to PHP 7, but the point is, this package states it supports PHP 5.6 in the composer.json file. So it should either be updated to reflect its actual PHP support (7.1+) or we need to look at a solution that works in both versions