Fix usage of inherited Sinatra::Base classes keyword arguments

lib/sinatra/base.rb

@@ -1522,8 +1522,8 @@ def prototype
       # Create a new instance of the class fronted by its middleware
       # pipeline. The object is guaranteed to respond to #call but may not be
       # an instance of the class new was called on.
-      def new(*args, &bk)
-        instance = new!(*args, &bk)
+      def new(*args, **kwargs, &bk)
+        instance = kwargs.length > 0 ? new!(**kwargs, &bk) : new!(*args, &bk)
         Wrapper.new(build(instance).to_app, instance)
       end
 

test/base_test.rb

@@ -6,6 +6,14 @@ class TestApp < Sinatra::Base
       get('/') { 'Hello World' }
     end
 
+    class TestKeywordArgumentInitializerApp < Sinatra::Base
+      def initialize(argument:)
+        @argument = argument
+      end
+
+      get('/') { "Hello World with Keyword Arguments: #{@argument}" }
+    end
+
     it 'include Rack::Utils' do
       assert TestApp.included_modules.include?(Rack::Utils)
     end
@@ -48,6 +56,16 @@ class TestApp < Sinatra::Base
       TestApp.configure { context = self }
       assert_equal self, context
     end
+
+    it "allows constructor to receive keyword arguments" do
+      app = TestKeywordArgumentInitializerApp.new(argument: "some argument")
+      request = Rack::MockRequest.new(app)
+
+      response = request.get('/')
+
+      assert response.ok?
+      assert_equal 'Hello World with Keyword Arguments: some argument', response.body
+    end
   end
 
   describe "Sinatra::Base#new" do