private method `gsub' called for false:FalseClass (NoMethodError)

/home/mini/ruby/lib/ruby/1.8/cgi.rb:362:in `escapeHTML'
(erb):13:in `do_eval_rhtml'
/usr/local/httpd/htdocs/mini/diary/tdiary.rb:898: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