unavailable on "[Plugin: Google XML Sitemaps] Prevent empty sitemaps"

I chose to exclude posts in certain categories from appearing in sitemaps.

Now, if the only posts within a month were in the excluded category, the plugin generates an empty child sitemap, and Google shows errors (urlset contains no urls).

1. Is there a way to prevent empty sitemaps from being generated?
2. Is there a way to manually remove offending child maps from the main map?

Any advice would be appreciated. Thank you.

http://wordpress.org/extend/plugins/google-sitemap-generator/