Null check before using get_class()

[romain-jacquart]

As of PHP 7.2, get_class() parameter can not be null.

This PR adds a simple null check before using get_class().

[GromNaN]

Hello @Anahkiasen this small fix makes your library compatible with PHP 7.2.

[Anahkiasen]

I'm sorry, the package is abandoned in favor of Spatie's. We indicated it on Packagist but not in the repository yet, we'll update the README to reflect this.

[GromNaN]

This is totally fine to want to stop maintaining a package and thank you for pointing to an alternative, unfortunately it is not compatible with PHP 5.6.
We are upgrading a project from PHP 5.6 to 7.2. We makes an heavy usage of your snapshot library and we have to keep these tests to validate the upgrade.
Our code must be compatible with both PHP versions during several weeks. We will eventually switch to spatie/phpunit-snapshot-assertions later.