--- mysql-5.5.29/mysys/my_getopt.c	2012-08-29 01:50:46.000000000 -0700
+++ mysql-5.5.29/mysys/my_getopt.c	2013-01-09 00:57:10.020208478 -0800
@@ -642,6 +642,13 @@
 
   if (!argument)
     argument= enabled_my_option;
+  
+  if(strlen(argument) == 0) {
+    my_getopt_error_reporter(ERROR_LEVEL,
+                             "%s: Empty value of '%s' is specified. Keep the previous value unchanged",
+                             my_progname, opts->name);  
+    return 0;
+  }
 
   if (value)
   {