Fix error when nil is passed to inflection code.

Author: magnars

clj-refactor.el

@@ -3359,13 +3359,14 @@ See: https://github.com/clojure-emacs/clj-refactor.el/wiki/cljr-create-fn-from-e
       (cljr--insert-example-fn fn-name args path))))
 
 (defun cljr--inflect-last-word (f s)
-  (save-match-data
-    (let* ((words (split-string s "-"))
-           (last-word (car (last words)))
-           (prefix (butlast words)))
-      (mapconcat 'identity
-                 (append prefix (list (funcall f last-word)))
-                 "-"))))
+  (when s
+    (save-match-data
+      (let* ((words (split-string s "-"))
+             (last-word (car (last words)))
+             (prefix (butlast words)))
+        (mapconcat 'identity
+                   (append prefix (list (funcall f last-word)))
+                   "-")))))
 
 (defun cljr--create-fn-from-list-fold (args path)
   (cljr--insert-example-fn (car args)