Since there is nowhere on the UI for this users to be displayed, and they are shown in the form of a pop-up box, I think it'd be meaningless to pop up to the user "oh and this won't work because you don't have a model set..." because the simulation cannot work at all if no model is set. 

And in OpenStudio, which shares this code, the model is always set.

That was my take on it anyhow, but it's also already been long enough since I developed this code it's hard to remember the exact line of thinking.