问获取未初始化的常量Twilio::REST::RequestError

EN

gem 'twilio-ruby', '~> 5.0.0.rc4'

app/controllers/home_controller.rb:59:in `rescue in call'

require "rubygems"
require "twilio-ruby"

def call
  @twilio = Twilio::REST::Client.new account_sid, auth_token

  begin
    @call = @twilio.account.calls.create({
     :to => , 
      :from => twilio_number,
      :url => url,
      :method => "GET",
      :if_machine => "Hangup",
      :timeout => "20"
    })

    # Getting current call status (seems like error here...!)
    get_status(@call.sid)

  rescue Twilio::REST::RequestError => error
    @err_msg = error.message
    puts @err_msg
    #returned error is like below:
    #NameError (uninitialized constant Twilio::REST::RequestError)
  end
end

def get_status(sid)
  @twilio = Twilio::REST::Client.new account_sid, auth_token
  @call = @twilio.account.calls.get(sid)
  puts "Process Status : " + @call.status
  return @call.status
end