I took the Category Map Example and removed one country from the sample (Island).
When allAreas = False, Island just dissapears. Instead I've set allAreas = True and nullColor = 'none'.
There are two problems now:
First (more severe): I dont want null-Countries to have the same color as the sea. Setting nullColor to something else breaks everything else.
Second: Because the series is split, every country gets rendered multiple times (4 times in this example) which just adds unneccessary rendering and lower performance.