Refactor Hash.fetch usage to provide default values

Rather than explicitly running through if/else blocks, it's easier to
read if the default value is provided against the Hash method calls directly.

lib/logstash/outputs/email.rb

@@ -94,54 +94,15 @@ class LogStash::Outputs::Email < LogStash::Outputs::Base
   def register
     require "mail"
     if @via == "smtp"
-      debug = @options.include?("debug")
-      if !debug
-        debug = false
-      else
-        debug = @options.fetch("debug")
-      end
-      smtpIporHost = @options.include?("smtpIporHost")
-      if !smtpIporHost
-        smtpIporHost = "localhost"
-      else
-        smtpIporHost = @options.fetch("smtpIporHost")
-      end
-      domain = @options.include?("domain")
-      if !domain
-        domain = "localhost"
-      else
-        domain = @options.fetch("domain")
-      end
-      port = @options.include?("port")
-      if !port
-        port = 25
-      else
-        port = @options.fetch("port")
-      end
-      tls = @options.include?("starttls")
-      if !tls
-        tls = false
-      else
-        tls = @options.fetch("starttls")
-      end
-      pass = @options.include?("password")
-      if !pass
-        pass = nil
-      else
-        pass = @options.fetch("password")
-      end
-      userName = @options.include?("userName")
-      if !userName
-        userName = nil
-      else
-        userName = @options.fetch("userName")
-      end
-      authenticationType = @options.include?("authenticationType")
-      if !authenticationType
-        authenticationType = nil
-      else
-        authenticationType = @options.fetch("authenticationType")
-      end
+      debug = @options.fetch("debug", false)
+      smtpIporHost = @options.fetch("smtpIporHost", "localhost")
+      domain = @options.fetch("domain", "localhost")
+      port = @options.fetch("port", 25)
+      tls = @options.fetch("starttls", false)
+      pass = @options.fetch("password", nil)
+      userName = @options.fetch("userName", nil)
+      authenticationType = @options.fetch("authenticationType", nil)
+
       Mail.defaults do
         delivery_method :smtp , { :address   => smtpIporHost,
                                   :port      => port,