Jekyll 1.4 exiting with error "error: undefined method `published' for nil:NilClass"

[dtsn]

I have just upgraded my install of jekyll to version 1.4 (from 1.3.0). The site no longer builds and fails with the following stack trace:

Generating... /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/site.rb:175:in `block in read_posts': undefined method `published' for nil:NilClass (NoMethodError)
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/site.rb:174:in `each'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/site.rb:174:in `read_posts'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/site.rb:147:in `read_directories'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/site.rb:116:in `read'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/site.rb:37:in `process'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/command.rb:18:in `process_site'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/commands/build.rb:23:in `build'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/lib/jekyll/commands/build.rb:7:in `process'
from /Library/Ruby/Gems/2.0.0/gems/jekyll-1.4.0/bin/jekyll:77:in `block (2 levels) in <top (required)>'
from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/command.rb:180:in `call'
from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/command.rb:180:in `call'
from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/command.rb:155:in `run'
from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/runner.rb:402:in `run_active_command'
from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/runner.rb:78:in `run!'
from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/delegates.rb:7:in `run!'
from /Library/Ruby/Gems/2.0.0/gems/commander-4.1.5/lib/commander/import.rb:10:in `block in <top (required)>'

For now i've downgraded back to version 1.3.0. But any help in getting this problem fixed would be greatly appreciated. I've looked through the change log and can't see anything that would cause the site to stop building, however I am not a ruby developer.

[xiebaochun]

I have this problem too.