fix if tag don't have expected attribute

lib/mida/itemprop.rb

@@ -77,8 +77,9 @@ def extract_property_value
       element = @element.name
       if non_textcontent_element?(element)
         attribute = NON_TEXTCONTENT_ELEMENTS[element]
-        value = @element.attribute(attribute).value
-        url_attribute?(attribute) ? make_absolute_url(value) : value
+        if attribute_node = @element.attribute(attribute)
+          url_attribute?(attribute) ? make_absolute_url(attribute_node.value) : attribute_node.value
+        end
       else
         @element.inner_text.strip
       end

spec/fixtures_spec.rb

@@ -0,0 +1,15 @@
+require 'spec_helper'
+require 'mida'
+require 'pathname'
+
+describe Mida do
+  it "should work with all fixtures" do
+    url = "https://market.android.com/details?id=com.zeptolab.ctr.paid&hl=en"
+
+    documents = Pathname.new(__FILE__).dirname.join('fixtures').children
+    documents.each do |file|
+      doc = Mida::Document.new(file.read, url)
+      doc.items.should_not be_empty
+    end 
+  end
+end