Confusing error on non-existing friend import

[mtzguido]

$ cat ZZ.fst
module ZZ

friend IDontExist
$ cat ZZ.fsti
module ZZ

$ fstar.exe ZZ.fst
ZZ.fst(3,0-3,17): (Error 310) 'friend' declarations cannot refer to modules that lack interfaces
1 error was reported (see above)

"Cannot find module IDontExist" would be better