undefined method `add_comment' for nil:NilClass (NoMethodError)

H:/home/blog/tukubamiraishiina/tdiary/tdiary/defaultio.rb:40:in `restore_comment'
H:/home/blog/tukubamiraishiina/tdiary/tdiary/defaultio.rb:30:in `open'
H:/home/blog/tukubamiraishiina/tdiary/tdiary/defaultio.rb:30:in `restore_comment'
H:/home/blog/tukubamiraishiina/tdiary/tdiary/defaultio.rb:134:in `transaction'
H:/home/blog/tukubamiraishiina/tdiary/tdiary.rb:1680:in `initialize'
H:/home/blog/tukubamiraishiina/tdiary/index.rb:44:in `new'
H:/home/blog/tukubamiraishiina/tdiary/index.rb:44