libgit2sharp troubles

lg2s.cs

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using LibGit2Sharp;

namespace GitSharp
{
	class MainClass
	{
		public static void Main(string[] args)
		{
			if (args.Length < 2)
			{
				Console.WriteLine("Usage:");
				Console.WriteLine("\targ1: output dir\n\targ2: repo http url");
				return;
			}

			var outputDir = Path.Combine(Environment.CurrentDirectory, args[0]);

			if (Directory.Exists(outputDir))
				Directory.Delete(outputDir);
			else
				Directory.CreateDirectory(outputDir);

			Console.WriteLine("Output: {0}", outputDir);

			var repoSource = args[1];
			Console.WriteLine("Repo: {0}", repoSource);

			var path = Repository.Clone(repoSource, outputDir);
			Console.WriteLine("Valid repo? {0}", Repository.IsValid(outputDir));

			using (var repo = new Repository(path))
			{
				var origin = repo.Network.Remotes["origin"];
				repo.Network.Fetch(origin);
				repo.Reset(ResetMode.Hard, "origin/bleed");
				var master = repo.Branches["master"]; // Type is `Branch` from LibGit2Sharp
				var bleed = repo.Branches["bleed"];
				
				// Here is where the System.ArgumentNullException (not NRE) is thrown
				// This call is using Repository.Checkout(Branch branch, Signature signature = null) so it has a default for the second param
				repo.Checkout(master);
			}
		}
	}
}