Kill almost all mutants in Zero::Request:AcceptType

Killed 13 of 14 mutants. I will see later, how it's possible to kill the last
one.
I also fixed the return value of "preferred", if the in initialize given string
is empty. Fixed the default value here.

lib/zero/request/accept_type.rb

@@ -8,11 +8,8 @@ module Zero
 
       # create a new instance of AcceptType
       def initialize(string)
-        if string.nil?
-          @elements = []
-        else
-          @elements = parse_elements(string)
-        end
+        string = '*/*' if string.nil? or string.empty?
+        @elements = parse_elements(string)
       end
 
       # return the preferred type
@@ -30,7 +27,7 @@ module Zero
 
       # converts the accept string to a useable array
       # @param string the string containing media ranges and options
-      def parse_elements(string = '*/*')
+      def parse_elements(string)
         string.
           gsub(/\s/, '').
           split(MEDIA_TYPE_SEPERATOR).

spec/unit/request/accepttype/preferred_spec.rb

@@ -7,18 +7,23 @@ describe Zero::Request::AcceptType, '#preferred' do
   let(:foo)  { 'text/foo' }
   let(:lower_quality) { foo + ';q=0.5' }
   let(:default) { '*/*;q=0.1' }
+  let(:option)  { [foo + ';b=23', html].join(',') }
   let(:simple_accept)  { [html, json].join(',') }
   let(:quality_accept) { [html, lower_quality, default].join(',') }
   let(:random_accept)  { [lower_quality, default, html].join(',') }
   let(:lower_accept)   { [lower_quality, default].join(',') }
   
   context 'without mapping' do
-    it { subject.new(html).preferred.should           == html }
-    it { subject.new(json).preferred.should           == json }
-    it { subject.new(simple_accept).preferred.should  == html }
-    it { subject.new(quality_accept).preferred.should == html }
-    it { subject.new(random_accept).preferred.should  == html }
-    it { subject.new(lower_accept).preferred.should   == foo }
+    it { subject.new(html).preferred.should           == html  }
+    it { subject.new(json).preferred.should           == json  }
+    it { subject.new(option).preferred.should         == foo   }
+    it { subject.new(simple_accept).preferred.should  == html  }
+    it { subject.new(quality_accept).preferred.should == html  }
+    it { subject.new(random_accept).preferred.should  == html  }
+    it { subject.new(lower_accept).preferred.should   == foo   }
+    it { subject.new(nil).preferred.should            == '*/*' }
+    it { subject.new('').preferred.should             == '*/*' }
+    it { subject.new('text / html').preferred.should  == html  }
   end
 
 #  context 'with mapping' do