allow disabling session_secret

lib/sinatra/base.rb

@@ -1296,7 +1296,8 @@ module Sinatra
 
       def setup_sessions(builder)
         return unless sessions?
-        options = { :secret => session_secret }
+        options = {}
+        options[:secret] = session_secret if session_secret?
         options.merge! sessions.to_hash if sessions.respond_to? :to_hash
         builder.use Rack::Session::Cookie, options
       end

test/helpers_test.rb

@@ -313,6 +313,20 @@ class HelpersTest < Test::Unit::TestCase
       assert_body 'ok'
     end
 
+    it 'allows disabling session secret' do
+      mock_app do
+        enable :sessions
+        disable :session_secret
+        get '/' do
+          assert !env['rack.session.options'].include?(:session_secret)
+          'ok'
+        end
+      end
+
+        get '/'
+        assert_body 'ok'
+    end
+
     it 'accepts an options hash' do
       mock_app do
         set :sessions, :foo => :bar