Hiki Error

uninitialized constant Hiki::Util::Diff (NameError)
/var/www/htdocs/rubygadgets/hiki/hiki/util.rb:170:in `unified_diff'
/var/www/htdocs/rubygadgets/hiki/misc/plugin/rss.rb:53:in `block in rss_body'
/var/www/htdocs/rubygadgets/hiki/misc/plugin/rss.rb:29:in `each'
/var/www/htdocs/rubygadgets/hiki/misc/plugin/rss.rb:29:in `rss_body'
/var/www/htdocs/rubygadgets/hiki/misc/plugin/rss.rb:86:in `rss'
/var/www/htdocs/rubygadgets/hiki/hiki/plugin.rb:231:in `send'
/var/www/htdocs/rubygadgets/hiki/hiki/command.rb:129:in `block in dispatch'
/usr/lib/ruby/2.7.0/timeout.rb:95:in `block in timeout'
/usr/lib/ruby/2.7.0/timeout.rb:33:in `block in catch'
/usr/lib/ruby/2.7.0/timeout.rb:33:in `catch'
/usr/lib/ruby/2.7.0/timeout.rb:33:in `catch'
/usr/lib/ruby/2.7.0/timeout.rb:110:in `timeout'
/var/www/htdocs/rubygadgets/hiki/hiki/command.rb:104:in `dispatch'
/var/www/htdocs/rubygadgets/ja/hiki.cgi:36:in `block in <main>'
/var/www/htdocs/rubygadgets/hiki/hiki/storage.rb:13:in `open_db'
/var/www/htdocs/rubygadgets/ja/hiki.cgi:34:in `<main>'