title: Rails 4 & mail-2.5.4 - NoMethodError: undefined method `ascii_only?' for nil:NilClass
body: <p>This error occurs on production server randomly not for every user. we are using sidekiq for delayed jobs and mandrill for emails. Please find the error backtrace form Airbrake.</p>
  
  <p>My ActionMailer Method is:</p>
  
  <pre><code>def auto_reply(email, subject, message)
      mail(to: email, body: message, subject: subject)
  end 
  
  /gems/mail-2.5.4/lib/mail/fields/common/parameter_hash.rb:44 in block in encoded
  /gems/mail-2.5.4/lib/mail/fields/common/parameter_hash.rb:43 in map
  /gems/mail-2.5.4/lib/mail/fields/common/parameter_hash.rb:43 in encoded
  /gems/mail-2.5.4/lib/mail/fields/content_type_field.rb:113 in encoded
  /gems/mail-2.5.4/lib/mail/field.rb:167 in method_missing
  /gems/mail-2.5.4/lib/mail/header.rb:206 in block in encoded
  /gems/mail-2.5.4/lib/mail/header.rb:205 in each
  /gems/mail-2.5.4/lib/mail/header.rb:205 in encoded
  /gems/mail-2.5.4/lib/mail/message.rb:1801 in encoded
  /gems/mail-2.5.4/lib/mail/body.rb:153 in block in encoded
  /gems/mail-2.5.4/lib/mail/parts_list.rb:11 in block in collect
  /gems/mail-2.5.4/lib/mail/parts_list.rb:11 in each
  /gems/mail-2.5.4/lib/mail/parts_list.rb:11 in collect
  /gems/mail-2.5.4/lib/mail/body.rb:153 in encoded
  /gems/mail-2.5.4/lib/mail/message.rb:1803 in encoded
  /gems/actionmailer-4.0.8/lib/action_mailer/base.rb:475 in set_payload_for_mail
  /gems/actionmailer-4.0.8/lib/action_mailer/base.rb:455 in block in deliver_mail
  /gems/activesupport-4.0.8/lib/active_support/notifications.rb:159 in block in instrument
  /gems/activesupport-4.0.8/lib/active_support/notifications/instrumenter.rb:20 in instrument
  /gems/activesupport-4.0.8/lib/active_support/notifications.rb:159 in instrument
  /gems/actionmailer-4.0.8/lib/action_mailer/base.rb:454 in deliver_mail
  /gems/mail-2.5.4/lib/mail/message.rb:232 in deliver
  /gems/sidekiq-3.2.4/lib/sidekiq/extensions/action_mailer.rb:20 in perform
  /gems/sidekiq-3.2.4/lib/sidekiq/processor.rb:52 in block (2 levels) in process
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/chain.rb:122 in call
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/chain.rb:122 in block in invoke
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/server/active_record.rb:6 in call
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/chain.rb:124 in block in invoke
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/server/retry_jobs.rb:74 in call
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/chain.rb:124 in block in invoke
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/server/logging.rb:11 in block in call
  /gems/sidekiq-3.2.4/lib/sidekiq/logging.rb:22 in with_context
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/server/logging.rb:7 in call
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/chain.rb:124 in block in invoke
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/chain.rb:127 in call
  /gems/sidekiq-3.2.4/lib/sidekiq/middleware/chain.rb:127 in invoke
  /gems/sidekiq-3.2.4/lib/sidekiq/processor.rb:51 in block in process
  /gems/sidekiq-3.2.4/lib/sidekiq/processor.rb:94 in stats
  /gems/sidekiq-3.2.4/lib/sidekiq/processor.rb:50 in process
  /gems/celluloid-0.16.0/lib/celluloid/calls.rb:26 in public_send
  /gems/celluloid-0.16.0/lib/celluloid/calls.rb:26 in dispatch
  /gems/celluloid-0.16.0/lib/celluloid/calls.rb:122 in dispatch
  /gems/celluloid-0.16.0/lib/celluloid/cell.rb:60 in block in invoke
  /gems/celluloid-0.16.0/lib/celluloid/cell.rb:71 in block in task
  /gems/celluloid-0.16.0/lib/celluloid/actor.rb:357 in block in task
  /gems/celluloid-0.16.0/lib/celluloid/tasks.rb:57 in block in initialize
  /gems/celluloid-0.16.0/lib/celluloid/tasks/task_fiber.rb:15 in block in create
  </code></pre>