#1 Visit a file: C-x C-f test.js
#2 Type this line: // emacs
#3 Put the cursor on the second slash and type M-q (fill-paragraph)
#4 Get an error: Wrong type argument: stringp, nil

Here's the debugger backtrace:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  looking-at(nil)
  c-literal-limits(nil t)
  c-mask-paragraph(t nil fill-paragraph nil)
  c-fill-paragraph(nil)
  js-c-fill-paragraph(nil)
  fill-paragraph(nil t)
  call-interactively(fill-paragraph nil nil)
  command-execute(fill-paragraph)

Thanks for your time.



In GNU Emacs 24.4.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.3)
 of 2014-10-21 on bitzer.hoetzel.info
Windowing system distributor `The X.Org Foundation', version 11.0.11602000
System Description:    Arch Linux

Configured using:
 `configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong
 --param=ssp-buffer-size=4' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Important settings:
  value of $LC_COLLATE: POSIX
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Javascript

Minor modes in effect:
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-x C-f t e s t . j s <return> <right> M-q <help-echo>
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo>
<help-echo> <menu-bar> <help-menu> <send-emacs-bug
-report>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
c-literal-limits: Wrong type argument: stringp, nil

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils js advice help-fns byte-opt bytecomp byte-compile
cconv json imenu thingatpt cc-mode cc-fonts easymenu cc-guess cc-menus
cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs time-date tooltip
electric uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
lisp-mode prog-mode register page menu-bar rfn-eshadow timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese hebrew greek romanian slovak czech european ethiopic
indian cyrillic chinese case-table epa-hook jka-cmpr-hook help simple
abbrev minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 99799 9585)
 (symbols 48 20607 0)
 (miscs 40 38 135)
 (strings 32 18066 4471)
 (string-bytes 1 618611)
 (vectors 16 12570)
 (vector-slots 8 422502 3583)
 (floats 8 64 268)
 (intervals 56 197 0)
 (buffers 960 12)
 (heap 1024 40578 947))