This method will return the value assigned via Mime::onGet. It is possible that a user
is attempting to mimic a magic property which would normally be accessed and provided
via the __get() method on the actual class. Since this method can contain logic, it
is also possible to have a Closure registered with Mime::give() on a property. As with
other mimicking, the Closure will be passed the mime object as the first and only
argument.