`respond_to_missing?` should fallback to `super` where method_missing could call `super`

actionmailer/lib/action_mailer/base.rb

@@ -580,7 +580,7 @@ def method_missing(method_name, *args)
       end
 
       def respond_to_missing?(method, include_all = false)
-        action_methods.include?(method.to_s)
+        action_methods.include?(method.to_s) || self
       end
     end
 

actionpack/lib/action_dispatch/http/mime_type.rb

@@ -298,7 +298,7 @@ def method_missing(method, *args)
       end
 
       def respond_to_missing?(method, include_private = false)
-        method.to_s.ends_with? "?"
+        (method.to_s.ends_with? "?") || super
       end
   end