class Roda::RodaPlugins::Flash::FlashHash

next hash if no argument is given.
next hash, or copy all entries from the current hash to the
Copy the entry with the given key from the current hash to the

def keep(key=(no_arg=true))
  if no_arg
    @next.merge!(self)
  else
    self[key] = self[key]
  end
end