Allow empty strings in code blocks (with ```) about pagedown HOT 2 CLOSED

Original markdown has such behavior too.

Triple-backtick codeblocks are not supported by Pagedown, they are not an 
originial Markdown feature, but an extension invented by GitHub (called "fenced 
codeblocks"): http://github.github.com/github-flavored-markdown/

We are currently considering to add it; see 
http://meta.stackoverflow.com/questions/125148/implement-style-markdown-code-blo
cks

But until that's the case, the behavior you're seeing is correct.