Merge from origin/emacs-26

fd50238 (origin/emacs-26) * doc/lispref/streams.texi (Output Variable...
769ea57 Use "GTK+" where applicable in the manual
5e69219 Document print-escape-control-characters
c00fea9 Merge branch 'emacs-26' of git.savannah.gnu.org:/srv/git/emac...
a2ab0d0 * doc/emacs/killing.texi (Rectangles): Don't use @key for cha...
6288c3d * lisp/emulation/viper.el: Unbreak it.
bf3535e More fixes in the Emacs manual
c87d04e Avoid aborts in 'md5'
9743f48 Mark keys consistently in manuals
ce557a9 Remove @key{} markups from @kindex entries in manuals
71243f0 * doc/emacs/display.texi (Standard Faces): Fix markup of inde...
7a069f3 Fix @kindex entries in manuals
6218933 Fix @cindex entries in manuals
57c9f12 Merge branch 'emacs-26' of git.sv.gnu.org:/srv/git/emacs into...
e415309 Fix @cindex entries in org.texi
560a23e Document reserved keys
105d085 * doc/misc/ebrowse.texi: Use @key{} for keys.

Conflicts:
	doc/misc/tramp.texi
	etc/NEWS

1 files changed, 3 insertions, 0 deletions

diff --git a/src/fns.c b/src/fns.c
index 47457e44c8e..ff1c0495693 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -4953,6 +4953,9 @@ extract_data_from_object (Lisp_Object spec,
 #endif
     }
 
+  if (!STRINGP (object))
+    signal_error ("Invalid object argument",
+                  NILP (object) ? build_string ("nil") : object);
   return SSDATA (object);
 }