From a8560fa361958b33d76e4468eb5c07d82a20196e Mon Sep 17 00:00:00 2001
From: Angelo capilleri <capilleri@yahoo.com>
Date: Wed, 31 Oct 2012 14:25:51 +0100
Subject: if format is unknown NullMimeTypeObject is returned

If a unknown format is passed in a request, the methods html?, xml?, json? ...etc
Nil Exception.

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

It refers to #7837, not fixes because it's not considered a improvement not a bug.
---
 actionpack/CHANGELOG.md                          |  5 +++++
 actionpack/lib/action_dispatch/http/mime_type.rb | 13 ++++++++++++-
 actionpack/test/dispatch/request_test.rb         | 12 +++++++++++-
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 48ba1518e0..cc042b5ac3 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Added `NullMimeTypeObject` class. This  allows to use html?, xml?, json?..etc when
+    the `format` of `request` is unknown.
+   
+    *Angelo  Capilleri*
+
 *   `date_select` helper accepts `with_css_classes: true` to add css classes similar with type
     of generated select tags.
 
diff --git a/actionpack/lib/action_dispatch/http/mime_type.rb b/actionpack/lib/action_dispatch/http/mime_type.rb
index 3d560518e1..5ee6f2056e 100644
--- a/actionpack/lib/action_dispatch/http/mime_type.rb
+++ b/actionpack/lib/action_dispatch/http/mime_type.rb
@@ -153,7 +153,7 @@ module Mime
       end
 
       def lookup_by_extension(extension)
-        EXTENSION_LOOKUP[extension.to_s]
+        EXTENSION_LOOKUP[extension.to_s] || NullMimeTypeObject.new
       end
 
       # Registers an alias that's not used on mime type lookup, but can be referenced directly. Especially useful for
@@ -301,6 +301,17 @@ module Mime
         method.to_s.ends_with? '?'
       end
   end
+
+  class NullMimeTypeObject
+    private
+    def method_missing(method, *args)
+      if method.to_s.ends_with? '?'
+        false
+      else
+        super
+      end
+    end
+  end
 end
 
 require 'action_dispatch/http/mime_types'
diff --git a/actionpack/test/dispatch/request_test.rb b/actionpack/test/dispatch/request_test.rb
index e2964f9071..b3466faffb 100644
--- a/actionpack/test/dispatch/request_test.rb
+++ b/actionpack/test/dispatch/request_test.rb
@@ -590,7 +590,17 @@ class RequestTest < ActiveSupport::TestCase
 
     request = stub_request
     request.expects(:parameters).at_least_once.returns({ :format => :unknown })
-    assert request.formats.empty?
+    assert_instance_of Mime::NullMimeTypeObject , request.format
+  end
+
+
+  test "format is not nil with unknown format" do
+    request = stub_request
+    request.expects(:parameters).at_least_once.returns({ format: :hello })
+    assert_equal request.format.html?, false
+    assert_equal request.format.xml?, false
+    assert_equal request.format.json?, false
+    assert !request.format.html?
   end
 
   test "formats with xhr request" do
-- 
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