fix backup bug
diff --git a/extendedcommands.c b/extendedcommands.c
index e7ffb8f..104957a 100644
--- a/extendedcommands.c
+++ b/extendedcommands.c
@@ -334,9 +334,10 @@
     }
 
     char cmd[PATH_MAX];
-    if (NULL == backup_name)
-        backup_name = "";
-    sprintf(cmd, "/sbin/nandroid-mobile.sh backup /sdcard/clockworkmod/backup/ %s", backup_name);
+    if (NULL != backup_name)
+    	sprintf(cmd, "/sbin/nandroid-mobile.sh backup /sdcard/clockworkmod/backup/ %s", backup_name);
+    else
+	sprintf(cmd, "/sbin/nandroid-mobile.sh backup /sdcard/clockworkmod/backup/");
     ui_print("Performing backup...\n");
     int ret = system(cmd);
     if (ret != 0)
@@ -474,4 +475,4 @@
         LOGE("Can't install update commands\n");
     }
     return run_script(argv[1]);
-}
\ No newline at end of file
+}