gcc-7 newly detects this class of bugs.
In this particular case it's clear that the inention was
to detect if the string is non-NULL *and* non-empty.


diff --git a/unique/uniqueapp.c b/unique/uniqueapp.c
index b40a86c..66a7226 100644
--- a/unique/uniqueapp.c
+++ b/unique/uniqueapp.c
@@ -176,7 +176,7 @@ set_startup_id (UniqueBackend *backend,
 {
   gchar *id;
 
-  if (startup_id && startup_id != '\0')
+  if (startup_id && *startup_id != '\0')
     id = g_strdup (startup_id);
   else
     {