return Mime::NullType if format is unknown

If a request has an unknown format, the methods html?, xml?, json? ...etc
not raise an Exception.

This patch add a class Mime::NullType, that is returned when  request.format is unknown
and it responds false to the methods that ends with '?' and true to 'nil?'.

It refers to #7837, this issue is considered a improvement not a bug.

1 files changed, 12 insertions, 1 deletions

diff --git a/actionpack/lib/action_dispatch/http/mime_type.rb b/actionpack/lib/action_dispatch/http/mime_type.rb
index f56f09c5b3..912da741b7 100644
--- a/actionpack/lib/action_dispatch/http/mime_type.rb
+++ b/actionpack/lib/action_dispatch/http/mime_type.rb
@@ -27,7 +27,7 @@ module Mime
   class << self
     def [](type)
       return type if type.is_a?(Type)
-      Type.lookup_by_extension(type)
+      Type.lookup_by_extension(type) || NullType.new
     end
 
     def fetch(type)
@@ -306,6 +306,17 @@ module Mime
       method.to_s.ends_with? '?'
     end
   end
+  
+  class NullType
+    def nil?
+      true
+    end
+
+    private
+    def method_missing(method, *args)
+      false if method.to_s.ends_with? '?'
+    end
+  end
 end
 
 require 'action_dispatch/http/mime_types'