helm-projectile-find-file lisp error (void-function string-empty-p)

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Expected behavior

triggers helm-projectile function triggers helm-projectile-find-file shouldn't fail. **helm-projectile.el needs to add (require 'subr-x) to the top.** string-empty-p is used in `helm-source-projectile-files-list` in helm-projectile.el ## Actual behavior Error out with (long lines truncated for brevity) ``` Debugger entered--Lisp error: (void-function string-empty-p) string-empty-p("") #[514 "r\302!\203\206p\211q\210\303 \304\305 \"!\306 !\20 apply(#[514 "r\302!\203\206p\211q\210\303 \304\305 \"!\306 helm-funcall-with-source(((name . "Projectile files") (candidates . #[0 "\301 \205 helm-process-filtered-candidate-transformer((("Gemfile" . "/Users/chris/git/helm-p helm-compute-matches(((name . "Projectile files") (candidates . #[0 "\301 \205;r helm--collect-matches((((name . "Project buffers") (init lambda nil (setq helm-pro helm-update(nil) helm-read-pattern-maybe("[helm-projectile-reproduce] pattern: " nil nil nil nil ni helm-internal((helm-source-projectile-buffers-list helm-source-projectile-files-li apply(helm-internal ((helm-source-projectile-buffers-list helm-source-projectile-f helm((helm-source-projectile-buffers-list helm-source-projectile-files-list helm-s apply(helm ((helm-source-projectile-buffers-list helm-source-projectile-files-list helm(:sources (helm-source-projectile-buffers-list helm-source-projectile-files-li helm-projectile(nil) funcall-interactively(helm-projectile nil) call-interactively(helm-projectile record nil) command-execute(helm-projectile record) helm-M-x(nil "helm-projectile") funcall-interactively(helm-M-x nil "helm-projectile") call-interactively(helm-M-x nil nil) command-execute(helm-M-x) ``` ## Steps to reproduce the problem M-x helm-projectile on any projectile project and I'd get the above error. M-x helm-projectile-find-file has the same issue. ## Backtraces if necessary (`M-x toggle-debug-on-error`) ## Environment & version information - `helm-projectile` version: 20180407.1842 - `helm` version (in `helm-pkg.el`): 20180413.335 - `projectile` version (`M-x projectile-version`): 20180324.2226 - Emacs version (`M-x emacs-version`): GNU Emacs 25.3.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21 Version 10.9.5 (Build 13F1911)) of 2017-09-12 - OS: Mac OS X 10.13.4 (17E199)