undefined method `empty?' for nil:NilClass (NoMethodError)

/usr/local/httpd/htdocs/mini/diary/tdiary.rb:107:in `shorten'
/usr/local/httpd/htdocs/mini/diary/tdiary.rb:75:in `join'
/usr/local/httpd/htdocs/mini/diary/tdiary.rb:75:in `safe'
/usr/local/httpd/htdocs/mini/diary/tdiary.rb:657:in `eval_src'
/usr/local/httpd/htdocs/mini/diary/tdiary.rb:904:in `do_eval_rhtml'
/usr/local/httpd/htdocs/mini/diary/tdiary.rb:854:in `eval_rhtml'
/usr/local/httpd/htdocs/mini/diary/index.rb:71