extract what little common code there was

app/workers/deliver_work_package_created_job.rb

@@ -28,19 +28,13 @@
 #++
 
 class DeliverWorkPackageCreatedJob
+  include MailNotificationJob
+
   def initialize(user_id, work_package_id)
     @user_id         = user_id
     @work_package_id = work_package_id
   end
 
-  def perform
-    notification_mail.deliver
-  end
-
-  def error(_job, e)
-    Rails.logger.error "notification of #{user.mail} failed (work package created): #{e}"
-  end
-
   private
 
   def notification_mail
@@ -52,6 +46,6 @@ class DeliverWorkPackageCreatedJob
   end
 
   def work_package
-    @journal ||= WorkPackage.find(@work_package_id)
+    @work_package ||= WorkPackage.find(@work_package_id)
   end
 end

app/workers/deliver_work_package_updated_job.rb

@@ -28,20 +28,14 @@
 #++
 
 class DeliverWorkPackageUpdatedJob
+  include MailNotificationJob
+
   def initialize(user_id, journal_id, current_user_id)
     @user_id         = user_id
     @journal_id      = journal_id
     @current_user_id = current_user_id
   end
 
-  def perform
-    notification_mail.deliver
-  end
-
-  def error(_job, e)
-    Rails.logger.error "notification of #{user.mail} failed (work package updated): #{e}"
-  end
-
   private
 
   def notification_mail

app/workers/mail_notification_job.rb

@@ -0,0 +1,48 @@
+#-- encoding: UTF-8
+#-- copyright
+# OpenProject is a project management system.
+# Copyright (C) 2012-2015 the OpenProject Foundation (OPF)
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See doc/COPYRIGHT.rdoc for more details.
+#++
+
+##
+# Requires including class to implement #notification_mail.
+module MailNotificationJob
+  def perform
+    notify
+  end
+
+  def notify
+    notification_mail.deliver
+  rescue ActiveRecord::RecordNotFound => e
+    # Since we cannot recover from this error we catch it and move on.
+    Rails.logger.error "Cannot deliver notification (#{self.inspect})
+                        as required record was not found: #{e}".squish
+  end
+
+  def error(_job, e)
+    Rails.logger.error "notification failed (#{self.inspect}): #{e}"
+  end
+end