When I try adding rack-flash to my sinatra app it stops working

Question

I've been using Rack::Flash for a while to display flash notices on responses in my Sinatra apps. Since I upgraded to Sinatra 1.3.2, the app crashes, logging the following whenever I make a request to the server:

!! Unexpected error while processing request: undefined method `<<' for nil:NilClass

The simplified code looks like this:

require 'sinatra'
require 'rack-flash'

enable :sessions
use Rack::Flash

get "/" do
  "Hello World"
end

Any idea why this could be happening?

Answer 1

rack-flash doesn't work with the latest versions of rack. Try sinatra-flash instead.