PHP 7 compatibility

[schmengler]

The following issue has been found in src/KJ/Magento/Util/Comparison/Filter/Null.php:

'null' is a reserved keyword as of PHP version 7.0 and should not be used to name a class, interface or trait or as part of a namespace

[kalenjordan]

Doh! Got it thanks. Man I haven't worked on this for so long....I wonder if someone might want to PR the fix or maybe even take over the repo...?