500 Internal Server Error

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

./tdiary/defaultio.rb:48:in `restore_comment'
./tdiary/defaultio.rb:39:in `each'
./tdiary/defaultio.rb:39:in `restore_comment'
./tdiary/defaultio.rb:37:in `open'
./tdiary/defaultio.rb:37:in `restore_comment'
./tdiary/defaultio.rb:154:in `transaction'
./tdiary.rb:1873:in `initialize'
index.rb:52:in `new'
index.rb:52