Do not raise when no attributes are given

lib/onelogin/saml/response.rb

@@ -50,6 +50,8 @@ def attributes
         result = {}
 
         stmt_element = REXML::XPath.first(document, "/p:Response/a:Assertion/a:AttributeStatement", { "p" => PROTOCOL, "a" => ASSERTION })
+        return {} if stmt_element.nil?
+
         stmt_element.elements.each do |attr_element|
           name  = attr_element.attributes["Name"]
           value = attr_element.elements.first.text

test/ruby-saml_test.rb

@@ -38,7 +38,7 @@ class RubySamlTest < Test::Unit::TestCase
       response = Onelogin::Saml::Response.new(response_document_3)
       assert !response.name_id.nil?
     end
-    
+
     should "check time conditions" do
       response = Onelogin::Saml::Response.new(response_document)
       assert !response.check_conditions
@@ -111,6 +111,11 @@ class RubySamlTest < Test::Unit::TestCase
         response = Onelogin::Saml::Response.new(response_document_3)
         assert_equal "[email protected]", response.attributes["http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress"]
       end
+
+      should "not raise on responses without attributes" do
+        response = Onelogin::Saml::Response.new(response_document_4)
+        assert_equal Hash.new, response.attributes
+      end
     end
 
     context "#session_expires_at" do