can't convert nil into Hash

boot.rb

require 'rubygems'

require 'yaml'
YAML::ENGINE.yamler= 'syck'

# Set up gems listed in the Gemfile.
ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)

require 'bundler/setup' if File.exists?(ENV['BUNDLE_GEMFILE'])

shell

% bundle exec rake db:setup --trace
** Invoke db:setup (first_time)
** Invoke db:create (first_time)
** Invoke db:load_config (first_time)
** Invoke rails_env (first_time)
** Execute rails_env
** Execute db:load_config
rake aborted!
can't convert nil into Hash
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:196:in `merge!'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:196:in `block in visit_Psych_Nodes_Mapping'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:190:in `each'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:190:in `each_slice'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:190:in `visit_Psych_Nodes_Mapping'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/visitor.rb:7:in `accept'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:16:in `accept'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:205:in `block in visit_Psych_Nodes_Mapping'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:190:in `each'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:190:in `each_slice'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:190:in `visit_Psych_Nodes_Mapping'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/visitor.rb:7:in `accept'
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:16:in `accept'
...

root@ypchen-ubuntu:~/octopress# rake generate

Generating Site with Jekyll

unchanged sass/screen.scss
/usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:in parse': couldn't parse YAML at line 20 column 0 (Psych::SyntaxError) from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:inparse_stream'
from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:119:in parse' from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:106:inload'
from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:205:in load_file' from /usr/local/rvm/gems/ruby-1.9.2-p290/gems/jekyll-0.11.0/lib/jekyll.rb:119:inconfiguration'
from /usr/local/rvm/gems/ruby-1.9.2-p290/gems/jekyll-0.11.0/bin/jekyll:207:in <top (required)>' from /usr/local/rvm/gems/ruby-1.9.2-p290/bin/jekyll:19:inload'
from /usr/local/rvm/gems/ruby-1.9.2-p290/bin/jekyll:19:in `

'

I couldn't generate the octopress blog