helpers not found in rescue_from

[binary1101]

class API < Grape::API
  format :json
  helpers do
    def server_error!
      error!({ error: 'Server error.' }, 500, { 'Content-Type' => 'text/error' })
    end
  end

  rescue_from :all do |e|
    server_error!
  end

  get :test do
    fail 'test'
  end
end

Started GET "/api/test" for 127.0.0.1 at 2016-02-23 13:01:51 +0600

NoMethodError (undefined method `server_error!' for #<Grape::Middleware::Error:0x007fcf830dbb28>):
  app/api/api.rb:13:in `block in <class:API>'

[dblock]

This was implemented in #1232, hasn't shipped yet, but works on HEAD.