class Roda::RodaPlugins::TypecastParams::Params

the given +klass+.
and only String values should be converted by calling +parse+ on
Helper for conversion methods where '' should be considered nil,

def parse!(klass, v)
  case v
  when ''
    nil
  when String
    klass.parse(v)
  else
    raise Error, "unexpected value received: #{v.inspect}"
  end
end