[xmonad] CycleRecentWS with nonempty workspaces only

[Ralph Hofmann]

I would like to have cycleRecentWS of XMonad.Actions.CycleRecentWS to
cycle the nonempty workspaces only. Can anybody point my the way to
achieve this? (The conventional if-then stuff is a mystery in
haskell;-))

Thanks in advance.

Ralph