Add default value for header

lib/zero/response.rb

@@ -11,6 +11,7 @@ module Zero
     #
     def initialize
       @status = 200
+      @header = {}
     end
 
     # Sets the status.

spec/unit/response/response_spec.rb

@@ -29,4 +29,10 @@ describe Zero::Response, '#status' do
   it "must return 200, if no status code was set" do
     subject.status.should eq(200)
   end
-end
+end
+
+describe Zero::Response, '#header' do
+  it "must return an empty hash, if no header was set" do
+    subject.header.should eq({})
+  end
+end