Estou usando a API HTTP do Mailgun para enviar e-mails do aplicativo rails, mas não consigo processar as visualizações do remetente. Esta é a minha classe de mala direta.

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  

Mas isso joga:

NoMethodError: método indefinido `each_byte 'para nil: NilClass

Como uso as visualizações de mala direta com a API Mailgun.

PS: Eu sei que existem muitas gemas disponíveis para usar o mailgun com trilhos, mas nenhuma delas oferece funcionalidade completa como a API.

Se houver alguma maneira alternativa de enviar e-mails da API usando as visualizações rails, estou aguardando a resposta. Só não sei como fazer isso (mesmo que não use o actionmailer)

Rastreio de erro COMPLETO

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'