This sounds very illegal. From what I know, in France the notice period is 1 month if it is "meublé", or 3 months if the appartment is empty.
Edit: actually, I just checked and that's for tenants. If the landlord wants to break the contract to sell the property, it's 3 months for "meublé", 6 months otherwise.
Edit: actually, I just checked and that's for tenants. If the landlord wants to break the contract to sell the property, it's 3 months for "meublé", 6 months otherwise.