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.

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 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'