Conform to the rack specs, with help from Rack::Lint

middleman-core/lib/middleman-core/core_extensions/request.rb

@@ -1,6 +1,7 @@
 # Built on Rack
 require "rack"
 require "rack/file"
+require "rack/lint"
 
 module Middleman
   module CoreExtensions
@@ -75,6 +76,8 @@ module Middleman
         def to_rack_app(&block)
           inner_app = inst(&block)
 
+          app.use Rack::Lint
+
           (@middleware || []).each do |m|
             app.use(m[0], *m[1], &m[2])
           end

middleman-more/lib/middleman-more/extensions/asset_hash.rb

@@ -66,7 +66,7 @@ module Middleman
           status, headers, response = @rack_app.call(env)
 
           # We don't want to use this middleware when rendering files to figure out their hash!
-          return [status, headers, response] if env["bypass_asset_hash"]
+          return [status, headers, response] if env["bypass_asset_hash"] == 'true'
 
           path = @middleman_app.full_path(env["PATH_INFO"])
           dirpath = Pathname.new(File.dirname(path))