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

(plugin/tb-show.rb):146:in `trackbacks_of_today_long'
./tdiary.rb:92:in `join'
./tdiary.rb:92:in `safe'
./tdiary.rb:697:in `eval_src'
./tdiary.rb:1033:in `do_eval_rhtml'
./tdiary.rb:975:in `eval_rhtml'
index.rb:73