Debugging regression for conflicting param types

In Rails 2.1.x (and possibly 2.2.x but I don't have an app to test) if you pass conflicting parameter types like ?x=&x[y]= we get a stack trace with helpful information:

Conflicting types for parameter containers. Expected an instance of Hash but found an instance of String. This can be caused by colliding Array and Hash parameters like qs[]=value&qs[key]=value. (The parameters received were "".)

In 2.3 (and maybe 2.2) we get something much less helpful, making the problem potentially difficult to track down:

/!\ FAILSAFE /!\ 2009-03-27 Status: 500 Internal Server Error You have a nil object when you didn't expect it! The error occurred while evaluating nil.each_pair

/usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/core_ext/hash/indifferent_access.rb:46:in `update'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/core_ext/hash/indifferent_access.rb:91:in `merge'
/usr/lib/ruby/gems/1.8/gems/actionpack-2.3.2/lib/action_controller/request.rb:381:in `parameters'

...

Nowhere in the stack trace does it point to a line of your application's code, and nowhere is there a hint that such a pair of parameters has sneaked in. Hopefully this doesn't come up often, but given the previous existence of such a useful error message, I imagine I'm not the first person to do this and have to spend time tracking it down, so it would be nice to have this back.