Commenting empty lines

[ludvig-faddeev]

Have made a keybinding for commenting lines like this

(global-set-key (kbd "C-;") (kbd "C-x C-;"))

This means that hitting "C-;" multiple times will comment and uncomment the 
line.

But when there is an empty line I want to insert the comment symbol, because
using "C-;" does not introduce the comment mark.