When you had a synched Eloquent model (e.g. without changed values) but
one of those values is `null`, then that value would be considered as
dirty. `Eloquent::changed` returns false, but the value is present in
`Eloquent::get_dirty`.
This fix makes sure that a `null` value in `$attributes` is only
present in `get_dirty` when it wasn't at all *set* in `$original`.
When running an Artisan task from within your application using `Command::run`, it fails when the same task is ran more than once. Every time the task is resolved, its file is included using `require` leading to duplicate class definitions. By using `require_once` this problem is avoided.
JoostK