InvalidPropertyPrefix error class

Raise a InvalidPropertyPrefix error if the prefix is invalid.

lib/microformats2.rb

@@ -33,4 +33,7 @@ module Microformats2
       html
     end
   end # class << self
+
+  class InvalidPropertyPrefix < StandardError; end
+
 end

lib/microformats2/format.rb

@@ -37,6 +37,7 @@ module Microformats2
       prefix = property_class.split("-").first
       # find ruby class for kind of property
       klass = Microformats2::Property::PREFIX_CLASS_MAP[prefix]
+      raise InvalidPropertyPrefix unless klass
       # We don't have a nokogiri element so pass in nil
       property = klass.new(nil, property_class, value)
       assign_property(property)

spec/lib/microformats2/collection_spec.rb

@@ -76,17 +76,22 @@ describe Microformats2::Collection do
 
       describe "Format.add_property" do
         let(:value) { "bar" }
-        before do
-          @collection.first.add_property("p-foo", value)
-        end
 
         it "creates the attr" do
+          @collection.first.add_property("p-foo", value)
           @collection.first.foo.to_s.should == value
         end
 
         it "allows json output of the attribute" do
+          @collection.first.add_property("p-foo", value)
           @collection.first.to_json.should include(value)
         end
+
+        it "raises a InvalidPropertyPrefix error if the prefix is invalid" do
+          expect {
+            @collection.first.add_property("xxx-foo", value)
+          }.to raise_error Microformats2::InvalidPropertyPrefix
+        end
       end
     end