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/hiki/command.rb:376:in `rescue in cmd_diff'
/var/www/htdocs/rubygadgets/hiki/hiki/command.rb:371:in `cmd_diff'
/var/www/htdocs/rubygadgets/hiki/hiki/command.rb:131: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>'