ROR actionmailer中nil：NilClass的未定義方法'charset ='

Question

我嘗試發送基本電子郵件，但ROR給我發了一個錯誤：

undefined method `charset=' for nil:NilClass

我的課 ：

class MonitoringAlertMailer < ActionMailer::Base
    default from: "myadmin@myadmin.com"    
   def monitoring_alert
            mail( to: 'myemail@email.com',     body: 'test',   content_type: "text/html",    subject: "test")
    end
end

錯誤來自：

ruby-2.3.1/gems/actionmailer-5.0.0.1/lib/action_mailer/base.rb:808:in `mail'


 def mail(headers = {}, &block)
      return message if @_mail_was_called && headers.blank? && !block

      # At the beginning, do not consider class default for content_type
      content_type = headers[:content_type]

      headers = apply_defaults(headers)

      # Apply charset at the beginning so all fields are properly quoted
      message.charset = charset = headers[:charset]

消息對象為零的地方請注意，當我發送帶有測試代碼的電子郵件時，它工作良好

ActionMailer::Base.mail(
  from: "test@example.co", 
  to: "valid.recipient@domain.com", 
  subject: "Test", 
  body: "Test"
).deliver

先感謝您

Answer 1

經過2天的調試。 從rails'，'〜> 5.0.0'升級到rails'，'〜> 5.0.1'