What is the duty of an invader to prevent damage from ice on the parking lot?

Was the ice on the parking-lot an unusual danger? The duty of an invitor to an invitee is set out in the oft quoted passage from the decision of Willes J. in Indermaur v. Dames (1866), L.R. 1 C.P. 274 at p. 288, where he said: And, with respect to such a visitor at least, we consider it settled law, that he, using reasonable care on his part for his own safety, is entitled to expect that the occupier shall on his part use reasonable care to prevent damage from unusual danger, which he knows or ought to know ...