Fix an issue with empty string warning

Hey,
I had this plugin in mind, glad that you made it. I addressed a small issue when post is empty.

Great job :thumbsup: 

![screen shot 2013-10-10 at 10 21 23 pm](https://f.cloud.github.com/assets/1505631/1308332/ad46bad2-31cc-11e3-866c-365701eff598.png)