500 Internal Server Error

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

./tdiary/wiki_style.rb:90:in `do_html4'
./tdiary/wiki_style.rb:79:in `html4'
./tdiary/blogwiki_style.rb:54:in `to_html4'
./tdiary/wiki_style.rb:412:in `each_section'
./tdiary/wiki_style.rb:411:in `each'
./tdiary/wiki_style.rb:411:in `each_section'
./tdiary/blogwiki_style.rb:49:in `to_html4'
./tdiary/wiki_style.rb:441:in `to_html'
(erb):7:in `eval_rhtml'
./tdiary.rb:398:in `eval_rhtml'
(erb):31:in `do_eval_rhtml'
./tdiary.rb:1659:in `each_day'
./tdiary.rb:1656:in `each'
./tdiary.rb:1656:in `each_day'
(erb):30:in `do_eval_rhtml'
./tdiary.rb:1089:in `do_eval_rhtml'
./tdiary.rb:1037:in `eval_rhtml'
index.rb:74