fix unknown mime type errors

config/initializers/mime_type_fix.rb

@@ -0,0 +1,21 @@
+module ActionDispatch
+  module Http
+    module MimeNegotiation
+
+      # Patched to always accept at least HTML
+      def accepts
+        @env["action_dispatch.request.accepts"] ||= begin
+          header = @env['HTTP_ACCEPT'].to_s.strip
+
+          if header.empty?
+            [content_mime_type]
+          else
+            Mime::Type.parse(header) << Mime::HTML
+          end
+        end
+      end
+
+    end
+  end
+end
+