class Opal::Sprockets::Server::Index

def html
  if @index_path
    raise "index does not exist: #{@index_path}" unless File.exist?(@index_path)
    Tilt.new(@index_path).render(self)
  else
    raise "Main asset path not configured (set 'main' within Opal::Server.new block)" if @server.main.nil?
    source
  end
end