Funny, mine has just dropped off as well (2007 Vision 44) after I removed the catch to see if I could fix the broken spring (I can't). Like you, I found it hollow, even though it obviously has a hole intended for foam injection - pretty useless. I've bought a spray can of Bostic Expandafoam to fill the lid, then glue it back in place.
Anyone come up with other measures to increase the insulation around the deep (top-access) fridge? Any ideas appreciated...