(void-variable git-commit-mode-map)

[chxp]

After install git-gutter+ and write add (global-git-gutter+-mode) to .emacs

it shows:

Debugger entered--Lisp error: (void-variable git-commit-mode-map)
  byte-code("\302\303\304\305#\210\306!\307\310\311#\210\307\312\313#\210\307\314\315#\210\307\316\317#\210\307\320\321#\210\307\322\323#\210\307\324\325#\210\307\326\327#\210\307\330\331#\210\211\262\332\333\334\335\336\337%\207" [git-commit-mode-map git-gutter+-commit-mode-map put git-gutter+-commit-mode derived-mode-parent git-commit-mode copy-keymap define-key "" git-gutter+-publish-commit "" git-gutter+-close-commit-edit-buffer "" git-gutter+-commit-toggle-amending "" git-gutter+-commit-toggle-allow-empty "" git-gutter+-commit-toggle-author "" git-gutter+-commit-toggle-date "" git-commit-ack [134217840] log-edit-previous-comment [134217838] log-edit-next-comment custom-declare-face git-gutter+-commit-header-face ((t :inherit font-lock-comment-face)) "Highlights the commit message header" :group git-gutter+-faces] 6)
  (global-git-gutter+-mode)
  eval-buffer(#<buffer  *load*-114986> nil "/home/chxp/syncthing/emacs/_emacs" nil t)  ; Reading at buffer position 9208
  load-with-code-conversion("/home/chxp/syncthing/emacs/_emacs" "/home/chxp/syncthing/emacs/_emacs" nil nil)
  load("/home/chxp/syncthing/emacs/_emacs" nil nil t)
  load-file("~/syncthing/emacs/_emacs")
  eval-buffer(#<buffer  *load*> nil "/home/chxp/.emacs" nil t)  ; Reading at buffer position 39
  load-with-code-conversion("/home/chxp/.emacs" "/home/chxp/.emacs" t t)
  load("~/.emacs" t t)
  #[0 "\205\262

So what I need to install addtionally? I tried git-commit-mode or git-auto-commit and so on, no one works