ubuntuで以下で落ちるのですが何ででしょう？

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
expand-file-name(nil "~/.navi2ch")
navi2ch-load-info(nil)
navi2ch-board-load-info(((name . #("芸スポ速報+" 0 6 (charset cp932-2-byte))) (bbstype . unknown) (uri . "https://hayabusa9.5ch.net/mnewsplus/";) (id . "mnewsplus") (type . board) (seen)))
navi2ch-board-select-board(((name . #("芸スポ速報+" 0 6 (charset cp932-2-byte))) (bbstype . unknown) (uri . "https://hayabusa9.5ch.net/mnewsplus/";) (id . "mnewsplus") (type . board) (seen)) nil)
navi2ch-bm-select-board(((name . #("芸スポ速報+" 0 6 (charset cp932-2-byte))) (bbstype . unknown) (uri . "https://hayabusa9.5ch.net/mnewsplus/";) (id . "mnewsplus") (type . board) (seen)) nil)
navi2ch-list-select-board(((name . #("芸スポ速報+" 0 6 (charset cp932-2-byte))) (bbstype . unknown) (uri . "https://hayabusa9.5ch.net/mnewsplus/";) (id . "mnewsplus") (type . board) (seen)) nil)
navi2ch-list-select-current-board(nil)
funcall-interactively(navi2ch-list-select-current-board nil)
call-interactively(navi2ch-list-select-current-board nil nil)
command-execute(navi2ch-list-select-current-board)