Vile zero error from hell

From IFWiki

A Vile Zero Error from Hell (VZEFH or V0EFH) is a particular sort of illegal instruction performed in the Z-Machine. Several opcodes manipulate objects in the game, performing such actions as moving objects, determining parents or children of objects, or looking up attributes or properties. Passing the object number 0, which refers to the non-object entity "nothing", is often inappropriate; most enlightened interpreters consider it an error (although rarely a fatal error) and will warn the user that the game file has performed an unusual operation. Developers attempt to avoid such problems, which, even though they are unlikely to damage player usability, make the work appear carelessly written.

Older editions of the Inform library and some third-party libraries are known to produce VZEFHs. VZEFHs most often occur when an object referred to by a variable are manipulated (i.e. x = parent(parasol); move x to MyFavoriteRoom -- if the parasol happens to have no parent, this is a VZEFH condition).