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, 10 insertions, 1 deletions

diff --git a/actionpack/test/dispatch/request_test.rb b/actionpack/test/dispatch/request_test.rb
index 263853fb6c..4e59e214c6 100644
--- a/actionpack/test/dispatch/request_test.rb
+++ b/actionpack/test/dispatch/request_test.rb
@@ -591,9 +591,18 @@ class RequestTest < ActiveSupport::TestCase
 
     request = stub_request
     request.expects(:parameters).at_least_once.returns({ :format => :unknown })
-    assert request.formats.empty?
+    assert_instance_of Mime::NullType, 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.nil?, true
+    assert_equal request.format.html?, false
+    assert_equal request.format.xml?, false
+    assert_equal request.format.json?, false
+  end
+  
   test "formats with xhr request" do
     request = stub_request 'HTTP_X_REQUESTED_WITH' => "XMLHttpRequest"
     request.expects(:parameters).at_least_once.returns({})