Recipe from "emacs -Q":

* Visit the attached file.
* Try to delete the second character in line 2.

At that moment, I see the following error:
  c-forward-name: Wrong type argument: integer-or-marker-p, nil

-- 
Dani Moncayo

In GNU Emacs 26.2 (build 1, x86_64-pc-cygwin)
 of 2019-04-15 built on moufang2
Repository revision: 3eb72f90eb994355ed13a136386f4cc0e1f7fd06
Windowing system distributor 'Microsoft Corp.', version 6.3.9600
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
c-forward-name: Wrong type argument: integer-or-marker-p, nil
Configured using:
 'configure
 --srcdir=/home/kbrown/src/cygemacs/emacs-26.2-1.x86_64/src/emacs-26.2
 --prefix=/usr --exec-prefix=/usr --localstatedir=/var --sysconfdir=/etc
 --docdir=/usr/share/doc/emacs --htmldir=/usr/share/doc/emacs/html -C
 --with-w32 'CFLAGS=-ggdb -O2 -pipe -Wall -Werror=format-security
 -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong
 --param=ssp-buffer-size=4
 -fdebug-prefix-map=/home/kbrown/src/cygemacs/emacs-26.2-1.x86_64/build=/usr/src/debug/emacs-26.2-1
 -fdebug-prefix-map=/home/kbrown/src/cygemacs/emacs-26.2-1.x86_64/src/emacs-26.2=/usr/src/debug/emacs-26.2-1'
 CPPFLAGS= LDFLAGS='

Configured features:
XPM JPEG TIFF GIF PNG IMAGEMAGICK SOUND DBUS GLIB NOTIFY ACL GNUTLS
LIBXML2 ZLIB TOOLKIT_SCROLL_BARS XIM THREADS LCMS2

Important settings:
  value of $LANG: C.ISO-8859-1
  locale-coding-system: iso-latin-1-unix

Major mode: C/*l

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-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
  abbrev-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
mml-sec password-cache epa derived epg epg-config gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils cc-mode cc-fonts easymenu cc-guess
cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs
cl-loaddefs cl-lib elec-pair time-date mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel disp-table
term/w32-win w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded 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 threads dbusbind gfilenotify w32 lcms2 multi-tty
make-network-process emacs)

Memory information:
((conses 16 117211 8204)
 (symbols 48 22508 2)
 (miscs 40 39 158)
 (strings 32 35475 1105)
 (string-bytes 1 1043992)
 (vectors 16 17218)
 (vector-slots 8 528979 11656)
 (floats 8 53 217)
 (intervals 56 368 226)
 (buffers 992 12))