Here, in my state, if one of your tags are stolen you need to replace both of them. That means going to the DMV and filling out a form and getting new tags.
Your question suggests that one tag is left on your car, and you never reported the tag stolen. So, how would the court know?
Below is a link to the florida stolen license plate database. Is your plate on this list?
And I've also put a link to request a replacement for a stolen plate.
If the parking citation was issued mere hours or days after the license plate was stolen from your vehicle, then you have an argument to be made in person. If longer, do not expect a break because there's really no excuse for not reporting it stolen after so many days pass.
Now, even if it had been a relatively short amount of time between the theft and the citation, to get officials to believe you, you would have to show proof of when the theft occurred. Is that doable. I think not.