[PATCH] ActiveResource::Base#id_from_response throws nil exception in some cases

patch file to fix responses without a "Location" header

When is the Location header nil? Also, please add tests to verify this behavior.

I think the Location header is nil whenever the reply from the server doesn't include one, which in a standard rails app seems to be any time the create request encountered an error. Thus a call to ActiveResource#create ends up sending a POST to a server, which may or may not choose to set the Location header. The standard "generate scaffold_resource" will produce something like this for the 'create' controller :

    respond_to do |format|
      if @entity.save
        flash[:notice] = 'Entity was successfully created.'
        format.html { redirect_to entity_url(@entity) }
        format.xml  { head :created, :location => entity_url(@entity) }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @entity.errors.to_xml }
      end
    end

Thus in the case of an error, no Location header is set. So the

  self.id = id_from_response(response)

call in ActiveResource#create will end up throwing the nil.

I'm new to the game of Tests, so it's taking me a bit of time to create a test to duplicate this, but I'm working it!

+1