bug#19521: 25.0.50; EDE show "Wrong type argument: stringp, nil" when there is a ".git" in the HOME directory

[孙林]

Dear Pals:

I got an error message "Wrong type argument: stringp, nil" when try to
open an file in my home directory. The issue can simply reproduce
on Emacs-25.0 (develop version) with follow steps:
1. mkdir ~/.git
2. emacs -q
3. eval (global-ede-mode) and (ede-enable-generic-projects) to enable EDE and 
the EDE generic projects.
4. eval (find-file "~/a.el")

The step 4 will produce the message. After `toggle-debug-on-error, the 
backtrace list follow:
Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  file-name-as-directory(nil)
  #[(this dir) "\306!\307\n\310\"\211;\205
  apply(#[(this dir) "\306!\307\n\310\"\211;\205
  ede-auto-detect-in-dir([object ede-project-autoload "generic-git" "Git" 
ede/generic ".git" nil nil unbound nil ede-generic-load ede-generic-vc-project 
t nil t] nil)
  ede--detect-ldf-root-predicate("~/")
  locate-dominating-file("~/" ede--detect-ldf-root-predicate)
  ede--detect-scan-directory-for-project-root("~/" [object ede-project-autoload 
"generic-git" "Git" ede/generic ".git" nil nil unbound nil ede-generic-load 
ede-generic-vc-project t nil t])
  ede-detect-directory-for-project("/proj/mtk06057/")
  ede-directory-project-cons("/proj/mtk06057/")
  ede-initialize-state-current-buffer()
  ede-minor-mode(1)
  ede-turn-on-hook()
  run-hooks(find-file-hook)
  after-find-file(t t)
  find-file-noselect-1(#<buffer a.el> "~/a.el" nil nil "~/a.el" nil)
  find-file-noselect("~/a.el" nil nil nil)
  find-file("~/a.el")
  eval((find-file "~/a.el") nil)
  eval-expression((find-file "~/a.el") nil)
  funcall-interactively(eval-expression (find-file "~/a.el") nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)

Please help investigate what's happened.

Best Regards
Lin Sun



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