Hiki Error

Accept-Charset encoding error (CGI::InvalidEncoding)
/usr/lib/ruby/2.5.0/cgi/core.rb:692:in `block (2 levels) in initialize_query'
/usr/lib/ruby/2.5.0/cgi/core.rb:687:in `each'
/usr/lib/ruby/2.5.0/cgi/core.rb:687:in `block in initialize_query'
/usr/lib/ruby/2.5.0/cgi/core.rb:686:in `each'
/usr/lib/ruby/2.5.0/cgi/core.rb:686:in `initialize_query'
/usr/lib/ruby/2.5.0/cgi/core.rb:870:in `initialize'
/usr/share/hiki/hiki/request.rb:15:in `new'
/usr/share/hiki/hiki/request.rb:15:in `initialize'
/usr/share/hiki/hiki.cgi:25:in `new'
/usr/share/hiki/hiki.cgi:25:in `<top (required)>'
/var/www/hiki/hiki.cgi:2:in `load'
/var/www/hiki/hiki.cgi:2:in `<main>'