use Proc.new to reduce some conditionals

Proc.new will pick up the passed in block, but since it's a default
param, it won't get evaluated unless someone doesn't pass in an app.  It
will raise an exception if no block is provided.

1 files changed, 1 insertions, 3 deletions

diff --git a/actionpack/lib/action_dispatch/middleware/stack.rb b/actionpack/lib/action_dispatch/middleware/stack.rb
index bbf734f103..87e627319e 100644
--- a/actionpack/lib/action_dispatch/middleware/stack.rb
+++ b/actionpack/lib/action_dispatch/middleware/stack.rb
@@ -112,9 +112,7 @@ module ActionDispatch
       middlewares.push(middleware)
     end
 
-    def build(app = nil, &block)
-      app ||= block
-      raise "MiddlewareStack#build requires an app" unless app
+    def build(app = Proc.new)
       middlewares.freeze.reverse.inject(app) { |a, e| e.build(a) }
     end