For historical reasons, man-db relies on being able to pass NULL
pointers to xstrdup. This patch was rejected by the Gnulib maintainers
on the basis that xfoo should only add out-of-memory checking to foo,
not other things. Accordingly, at some point we should migrate away from
this requirement and remove this patch.

=== modified file 'gnulib/lib/xmalloc.c'
--- gnulib/lib/xmalloc.c	2007-10-14 02:09:24 +0000
+++ gnulib/lib/xmalloc.c	2007-10-20 17:21:14 +0000
@@ -114,10 +114,12 @@
   return memcpy (xmalloc (s), p, s);
 }
 
-/* Clone STRING.  */
+/* If STRING is NULL, return NULL.  Otherwise, clone STRING.  */
 
 char *
 xstrdup (char const *string)
 {
+  if (!string)
+    return NULL;
   return xmemdup (string, strlen (string) + 1);
 }