Parse `doesnthave()` condition and add to cache key

[brunorsantos]

Issue

It has to be created cache for when tried to retrieve from a model, some result that we doesn't want a relationship attached.

For example: Authors that does not have books:
$authors = collect([(new Author)->doesntHave('books')->first()]);

Stack Trace

Currently, if we try to execute the method, we have this stack:

ErrorException: Undefined index: column

/home/vagrant/Code/laravel-model-caching/src/CachedBuilder.php:106
/home/vagrant/Code/laravel-model-caching/vendor/laravel/framework/src/Illuminate/Support/Collection.php:1197
/home/vagrant/Code/laravel-model-caching/src/CachedBuilder.php:107
/home/vagrant/Code/laravel-model-caching/src/CachedBuilder.php:28
/home/vagrant/Code/laravel-model-caching/src/CachedBuilder.php:203

[mikebronner]

Thanks for reporting the error. Caching should work with first(), looks like a bug crept in. Also, I don't think we are looking at the doesntHave() command when caching things, so that will need to be added.