->filterable() and filters doesn't work for null

[ziming]

sometimes the value of a Boolean field, BelongsTo or Select Field is null

Calling ->filterable() did not reveal that null choice. Hence it is a bug.

While when it comes to building manual filter, one has to do some trickery since array keys cannot be null. Like giving a choice with a key that has a string name or empty string then have a if statement to check it and apply null.

It will be great if it work seamlessly if I just specify ->nullable() or ->rules(['nullable'])