StaticFileHasher for c#

StaticFileHasher.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace MyUmbracWebsite
{
    public static class StaticFileHasher
    {
        private static Dictionary<string, string> FileHashes { get; set; }

        public static string Hash(string path)
        {
            if (String.IsNullOrEmpty(path) || !FileHashes.ContainsKey(path))
            {
                return null;
            }

            return FileHashes[path];
        }

        public static void HashFiles(params string[] directories)
        {
            FileHashes = new Dictionary<string, string>();
            var FileExtensions = new string[] { "*.css", "*.js", };

            using (var md5 = MD5.Create())
            {
                foreach (var directory in directories)
                {
                    foreach (var extension in FileExtensions)
                    {
                        foreach (var file in Directory.EnumerateFiles(directory, extension))
                        {
                            byte[] hash;

                            using (var stream = File.OpenRead(file))
                            {
                                hash = md5.ComputeHash(stream);
                            }

                            StringBuilder sOutput = new StringBuilder(hash.Length);
                            for (var i = 0; i < hash.Length - 1; i++)
                            {
                                sOutput.Append(hash[i].ToString("X2"));
                            }

                            FileHashes.Add(Path.GetFileName(file), sOutput.ToString().ToLower());
                        }
                    }
                }
            }
        }

    }
}