Should fix the problem reported by pressureman

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@8331 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/mod/languages/mod_lua/freeswitch_lua.cpp

@@ -130,7 +130,7 @@ void Session::setHangupHook(char *func, char *arg) {
 	
 	if (func) {
 		hangup_func_str = strdup(func);
-		if (arg) {
+		if (!switch_strlen_zero(arg)) {
 			hangup_func_arg = strdup(arg);
 		}
 		switch_channel_set_private(channel, "CoreSession", this);