error when sign with account facebook

Koala::Facebook::APIError (HTTP 500: Response body: {"error":{"message":"No node specified","type":"Exception"}}):
  app/models/user.rb:69:in `find_for_facebook_oauth'
  app/controllers/users/omniauth_callbacks_controller.rb:15:in `facebook'

in line 69 :
if  picture = @graph.get_picture(name)
      puts '11111111111111111111111111111111111111'
      picture
    end

in line 15: @user = User.find_for_facebook_oauth(env["omniauth.auth"], current_user)

I do wrong anything ?
thanks for help