I'm not arguing that. Completely disregarding the void document, you will still want to document _and notify_ the company that your IP is in the exempt category.

I'm assuming the law is similar to Kansas Statute 44-130[0]

(d) Even though the employee meets the burden of proving the conditions specified in this section, the employee shall disclose, at the time of employment or thereafter, all inventions being developed by the employee, for the purpose of determining employer and employee rights in an invention.

[0]: http://www.kslegislature.org/li_2014/b2013_14/statute/044_00...