【Rails】ArgumentError (SMTP To address may not be blank: []):の対処法【Mailer】

<h2>症状</h2>
RailsのActionMailerで送信先のメールアドレスを変更しようとした時に、下記エラーメッセージが表示されました。
翻訳すると、「ArgumentError（SMTP宛先アドレスを空白にすることはできません：[]）：」でした。

```terminal:error
[ActiveJob] [ActionMailer::MailDeliveryJob] [7112b19a-912c-49a9-b0ed-d7a83176ab57] Error performing ActionMailer::MailDeliveryJob (Job ID: 7112b19a-912c-49a9-b0ed-d7a83176ab57) from Async(mailers) in 1377.91ms: ArgumentError (SMTP To address may not be blank: []):      
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/check_delivery_params.rb:21:in 
`check_to'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/check_delivery_params.rb:7:in `check'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/network/delivery_methods/smtp_connection.rb:52:in `deliver!'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/network/delivery_methods/smtp.rb:101:in `block in deliver!'
C:/Ruby30-x64/lib/ruby/3.0.0/net/smtp.rb:558:in `start'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/network/delivery_methods/smtp.rb:109:in `start_smtp_session'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/network/delivery_methods/smtp.rb:100:in `deliver!'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/message.rb:2159:in `do_delivery'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/message.rb:260:in `block in deliver'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/actionmailer-6.0.4.1/lib/action_mailer/base.rb:589:in `block in deliver_mail'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/notifications.rb:180:in `block in instrument'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/notifications/instrumenter.rb:24:in `instrument'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/notifications.rb:180:in `instrument'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/actionmailer-6.0.4.1/lib/action_mailer/base.rb:587:in `deliver_mail'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/mail-2.7.1/lib/mail/message.rb:260:in `deliver'    
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/actionmailer-6.0.4.1/lib/action_mailer/message_delivery.rb:115:in `block in deliver_now'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/actionmailer-6.0.4.1/lib/action_mailer/rescuable.rb:17:in `handle_exceptions'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/actionmailer-6.0.4.1/lib/action_mailer/message_delivery.rb:114:in `deliver_now'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/actionmailer-6.0.4.1/lib/action_mailer/mail_delivery_job.rb:23:in `perform'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/execution.rb:40:in `block in perform_now'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:112:in `block in run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/i18n-1.8.10/lib/i18n.rb:314:in `with_locale'       
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/translation.rb:9:in `block (2 levels) in <module:Translation>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `instance_exec'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `block in run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/core_ext/time/zones.rb:66:in `use_zone'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/timezones.rb:9:in 
`block (2 levels) in <module:Timezones>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `instance_exec'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `block in run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/logging.rb:25:in `block (4 levels) in <module:Logging>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/notifications.rb:180:in `block in instrument'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/notifications/instrumenter.rb:24:in `instrument'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/notifications.rb:180:in `instrument'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/logging.rb:24:in `block (3 levels) in <module:Logging>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/logging.rb:45:in `block in tag_logger'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/tagged_logging.rb:80:in `block in tagged'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/tagged_logging.rb:28:in `tagged'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/tagged_logging.rb:80:in `tagged'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/logging.rb:45:in `tag_logger'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/logging.rb:21:in `block (2 levels) in <module:Logging>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `instance_exec'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `block in run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:139:in `run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/execution.rb:39:in `perform_now'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/execution.rb:25:in `block in execute'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:112:in `block in run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/railtie.rb:43:in `block (4 levels) in <class:Railtie>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/execution_wrapper.rb:88:in `wrap'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/reloader.rb:72:in `block in wrap'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/execution_wrapper.rb:88:in `wrap'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/reloader.rb:71:in `wrap'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/railtie.rb:42:in `block (3 levels) in <class:Railtie>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `instance_exec'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:121:in `block in run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:139:in `run_callbacks'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/execution.rb:23:in `execute'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activejob-6.0.4.1/lib/active_job/queue_adapters/async_adapter.rb:70:in `perform'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/concurrent-ruby-1.1.9/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:363:in `run_task'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/concurrent-ruby-1.1.9/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:352:in `block (3 levels) in create_worker'        
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/concurrent-ruby-1.1.9/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:335:in `loop'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/concurrent-ruby-1.1.9/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:335:in `block (2 levels) in create_worker'        
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/concurrent-ruby-1.1.9/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:334:in `catch'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/concurrent-ruby-1.1.9/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:334:in `block in create_worker'
```

以下が該当のソースになります。

```user_controller.rb
            #paramsにuser_idと送り先のメールアドレスであるnew_emailを受け取っている
            def send_change_email
                user = User.find_by(id: params[:user_id])

                UserMailer.with(user: user,new_email: params[:new_mail]).change_emailaddress_email.deliver_later         
            end
```

```ruby:user_mailer.rb
  def change_emailaddress_email
    @user = params[:user]
    @url  = 'http://example.com/login'
    @new_email = params[:new_email]
    mail(to: @new_email, subject: 'メールアドレス変更を完了させましょう')
  end
```

<h2>解決策</h2>
controllerのparams指定が間違っていたため、うまく送り先のメールアドレスが受け取れずに、ブランクを渡してしまい、ブランク宛てにメールを送ってしまっていたようです。(params[:new_mail]からparams[new_email]に)
ほぼほぼ翻訳通りの「宛先アドレスを空白にすることはできません」という内容でした。

```user_controller.rb
            #paramsにuser_idと送り先のメールアドレスであるnew_emailを受け取っている
            def send_change_email
                user = User.find_by(id: params[:user_id])

                UserMailer.with(user: user,new_email: params[:new_email]).change_emailaddress_email.deliver_later         
            end
```


<h2>参考</h2>

https://railsguides.jp/action_mailer_basics.html