Hide empty measures/ bars?

If I have a number of empty bars I want to hide them, i.e. contract them to a single bar with the number of bars indicated overhead. I I recall the shortcut used to be key 'M' and that would hide and unhide bars as required. That shortcut no longer seems to work. I have been able to hide the empty bars in a piece that I am writing by using stave/bar properties, but having hidden them I am unable to open them up again. Can anyone advise me what I am missing?