Zero equal divisions of the octave
There are two ways to approach this idea.
Given that n-edo means that you are dividing the octave into 1/n equal divisions and that 1/0 is sometimes considered undefined, it would follow that 0edo would be similarly undefined and thus would comprise no sounds at all (or intervals from unison are undefined, so 1 note is there).
The other way of looking at it is to see what happens as n gets smaller. At 1-edo you have one note per octave. At 0.5-edo you have 1/0.5 which is one note every two octaves. As n gets smaller you reach a point where you only have one note within an audible octave range and any other notes outside of this range. Taking this to its conclusion, and assuming you want 0edo to be defined, you would conclude that 0edo is just one note without any octaves.
An example of a trivial temperament, 0edo tempers out all commas and is consistent in all limits.