Я использую Mailgun HTTP API для отправки писем из приложения rails. Но я не могу отобразить почтовые сообщения. Это мой почтовый класс.

class MailgunMails < ActionMailer::Base

    def send_complex_message
      data = Multimap.new
      data[:from] = "Excited User <postmasters@#{@@domain}>"
      data[:to] = "[email protected]"
      data[:subject] = "Hello"
      data[:html] = File.open("#{Rails.root}/app/views/mailgun_mails/send_complex_message.html.erb", 'r').to_s.html_safe  
      ## also tried
      data[:html] = render(template: "send_complex_message.html.erb")
      response = RestClient.post "https://api:#{@@private_key}"\
      "@api.mailgun.net/v2/#{@@domain}/messages", data

      response = JSON.parse(response)

    end

end  

Но это бросает:

NoMethodError: неопределенный метод `each_byte 'для nil: NilClass

Как использовать почтовые представления с Mailgun API.

PS: я знаю, что есть много драгоценных камней для использования mailgun с рельсами, но ни один из них не дает полной функциональности, как API.

Если есть какой-либо альтернативный способ отправки электронных писем из API с использованием представлений Rails, я жду этого ответа. Я просто не знаю, как это сделать (даже если он не использует actionmailer)

ПОЛНАЯ ошибка трассировки

NoMethodError: undefined method `each_byte' for nil:NilClass
    from /Users/example/.rvm/rubies/ruby-2.0.0-p451/lib/ruby/2.0.0/uri/common.rb:307:in `block in escape'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/core_ext/string/output_safety.rb:177:in `gsub'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/core_ext/string/output_safety.rb:177:in `gsub'
    from /Users/example/.rvm/rubies/ruby-2.0.0-p451/lib/ruby/2.0.0/uri/common.rb:304:in `escape'
    from /Users/example/.rvm/rubies/ruby-2.0.0-p451/lib/ruby/2.0.0/uri/common.rb:623:in `escape'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:150:in `handle_key'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:143:in `block in build_stream'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:142:in `collect'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:142:in `build_stream'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:53:in `initialize'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:18:in `new'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:18:in `generate'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/request.rb:45:in `initialize'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/request.rb:33:in `new'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/request.rb:33:in `execute'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient.rb:72:in `post'
... 2 levels...
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/callbacks.rb:18:in `block in process_action'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/callbacks.rb:373:in `_run__1281843520849433682__process_action__callbacks'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/callbacks.rb:80:in `run_callbacks'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/callbacks.rb:17:in `process_action'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/base.rb:136:in `process'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/rendering.rb:44:in `process'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:503:in `process'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:497:in `initialize'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:480:in `new'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:480:in `method_missing'
    from (irb):1
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/railties-4.0.4/lib/rails/commands/console.rb:90:in `start'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/railties-4.0.4/lib/rails/commands/console.rb:9:in `start'
    from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/railties-4.0.4/lib/rails/commands.rb:62:in `<top (required)>'
    from bin/rails:4:in `require'