XML Sitemap Error after changing File System Path

I changed the path of my file system (always set to public) and copied all its content to the new directory with the proper permission. I also deleted the old directory. When I checked the sitemap at /sitemap.xml, it threw this error:
warning: fopen() [function.fopen]: Filename cannot be empty in /home/x/public_html/includes/file.inc on line 810.
I then realized there was a "Cache directory" field in XML sitemap.

I suggest there is some sort of validation before trying to open the file to throw a friendlier error message. Or to sync the cache directory to the file system directory.