Don't know exactly how nullification is relevant, despite doing a quick google search. Workplaces themselves can still implement ZERO TOLERANCE DRUG FREE policies, and anybody working for the gov't such as city or state employees are still subject to the same evaluations in place BEFORE anyone legalized marijuana and REGARDLESS if the state you live in has legalized it or not. FEDERAL law has not legalized it, therefore any workplace CAN/gov't workplaces WILL discriminate against users (even ones with "medical marijuana permits") as grounds for termination or ineligible for employment.
That being said, I think it should just be legal everywhere within moderation like alcohol, because putting people in jail for pot use is just silly and taking up resources that would better serve the rehabilitation of criminals that actually pose a threat to society.
I've been doing a little research on the subject and just wanted to enlighten those who may have been confused or misinformed.