*Backtrace*.txt

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  get-file-buffer(nil)
  org-find-base-buffer-visiting(nil)
  org-get-agenda-file-buffer(nil)
  org-refile-get-targets(nil (#("ferry" 0 5 (fontified t line-prefix nil wrap-prefix #("  " 0 2 (face org-indent)) face org-level-1))))
  org-refile-get-location("Refile subtree \"ferry\" to" nil confirm nil)
  org-refile(nil)
  #<subr call-interactively>(org-refile nil nil)
  ad-Advice-call-interactively(#<subr call-interactively> org-refile)
  apply(ad-Advice-call-interactively #<subr call-interactively> org-refile)
  call-interactively(org-refile)
  org-self-insert-command(1)
  #<subr call-interactively>(org-self-insert-command nil nil)
  ad-Advice-call-interactively(#<subr call-interactively> org-self-insert-command nil nil)
  apply(ad-Advice-call-interactively #<subr call-interactively> (org-self-insert-command nil nil))
  call-interactively(org-self-insert-command nil nil)
  command-execute(org-self-insert-command)