Don't create empty Namespace nodes.

lib/oga/xml/parser.y

@@ -338,8 +338,12 @@ Unexpected #{name} with value #{value.inspect} on line #{@line}:
   # @return [Oga::XML::Element]
   #
   def on_element(namespace, name, attributes = {})
+    if namespace
+      namespace = Namespace.new(:name => namespace)
+    end
+
     element = Element.new(
-      :namespace  => Namespace.new(:name => namespace),
+      :namespace  => namespace,
       :name       => name,
       :attributes => attributes
     )

spec/oga/xml/parser/elements_spec.rb

@@ -13,6 +13,10 @@ describe Oga::XML::Parser do
     example 'set the name of the element' do
       @element.name.should == 'p'
     end
+
+    example 'do not set a namespace' do
+      @element.namespace.nil?.should == true
+    end
   end
 
   context 'elements with namespaces' do