I'm posting this because some people don't seem to get it according to crash logs I read.
As documented in metadb.h (I'm moving this to titleformat.h and putting references to it in other headers) "extra_items" parameter is a list of null-separated strings, terminated with a double null character, like this:
Not including double null will of course lead to crashes, and looks like several third party components do that.
Extra_items pointer can be null, unless headers declaring particular API call state otherwise.