helm-gtags-find-tag-from-here error: apply: Wrong type argument: stringp, nil

[tuhdo]

Here is the backtrace:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  call-process("global" nil (t nil) nil "--result=grep" "--from-here=356:/home/xtuudoo/workspace/study/discrete_optimization/hw1/knapsack.cpp" nil)
  apply(call-process "global" nil (t nil) nil ("--result=grep" "--from-here=356:/home/xtuudoo/workspace/study/discrete_optimization/hw1/knapsack.cpp" nil))
  process-file("global" nil (t nil) nil "--result=grep" "--from-here=356:/home/xtuudoo/workspace/study/discrete_optimization/hw1/knapsack.cpp" nil)
  helm-gtags--find-tag-from-here-init()
  apply(helm-gtags--find-tag-from-here-init nil)
  helm-funcall-with-source(((name . "GNU Global at ~/workspace/study/discrete_optimization/hw1/") (helm-gtags-base-directory) (init . helm-gtags--find-tag-from-here-init) (candidates . helm-candidates-in-buffer) (action ("Open file" . helm-gtags--action-openfile) ("Open file other window" . helm-gtags--action-openfile-other-window)) (persistent-action . helm-gtags--persistent-action) (filtered-candidate-transformer helm-fuzzy-highlight-matches) (real-to-display . helm-gtags--candidate-transformer) (candidate-number-limit . 9999) (volatile) (match identity) (header-line . "C-j: helm-gtags--persistent-action (keeping session)") (dont-plug helm-compile-source--candidates-in-buffer helm-compile-source--match-plugin helm-compile-source--persistent-help) (matchplugin) (get-line . buffer-substring-no-properties) (search helm-mp-exact-search helm-mp-search helm-candidates-in-buffer-search-default-fn)) helm-gtags--find-tag-from-here-init)
  helm-funcall-foreach(init nil)
  helm-initial-setup(nil)
  helm-initialize(nil nil nil (helm-source-gtags-find-tag-from-here))
  #[0 "\311\211\211\211\305\206\n

[syohex]

Please check latest version(I have fixed at #113)