Getting Rack::Session::Abstract::SessionHash error with rails edge

I am getting Rack::Session::Abstract::SessionHash error with rails
edge when I start server.

Code works fine with rails 3.0.1 .

What's the fix?

Thank you all.

Use edge Rack from git repo:

gem 'rack', :git => 'git://github.com/rack/rack.git'

https://rails.lighthouseapp.com/projects/8994/tickets/5778-edge-rails-sends-include-to-uninitialized-constant-racksessionabstractsessionhash

For any googlers coming in:

I was getting the error:

Could not find gem ‘rack (~> 1.3.2)’, which is required by gem ‘rails (= 3.1.0.rc6)’, in any of the sources.

Which was fixed by:

gem ‘rack’, :git => ‘git://github.com/rack/rack.git’, :branch => ‘rack-1.3’

unfortunately, the underlying issue remains.