Convert byte array to string with the correct BOM, extension method

gistfile1.cs

public static class Extensions
{
	/// <summary>
	/// Converts a byte array to a string, using its byte order mark to convert it to the right encoding.
	/// Original article: http://www.west-wind.com/WebLog/posts/197245.aspx
	/// </summary>
	/// <param name="buffer">An array of bytes to convert</param>
	/// <returns>The byte as a string.</returns>
	public static string GetString(this byte[] buffer)
	{
		if (buffer == null || buffer.Length == 0)
			return "";
		
		// Ansi as default
		Encoding encoding = Encoding.Default;

		/*
		EF BB BF        UTF-8
		FF FE UTF-16    little endian
		FE FF UTF-16    big endian
		FF FE 00 00     UTF-32, little endian
		00 00 FE FF     UTF-32, big-endian
		*/
		if (buffer[0] == 0xef && buffer[1] == 0xbb && buffer[2] == 0xbf)
			encoding = Encoding.UTF8;
		else if (buffer[0] == 0xfe && buffer[1] == 0xff)
			encoding = Encoding.Unicode;
		else if (buffer[0] == 0xfe && buffer[1] == 0xff)
			encoding = Encoding.BigEndianUnicode; // utf-16be
		else if (buffer[0] == 0 && buffer[1] == 0 && buffer[2] == 0xfe && buffer[3] == 0xff)
			encoding = Encoding.UTF32;
		else if (buffer[0] == 0x2b && buffer[1] == 0x2f && buffer[2] == 0x76)
			encoding = Encoding.UTF7;
		using (MemoryStream stream = new MemoryStream())
		{
			stream.Write(buffer, 0, buffer.Length);
			stream.Seek(0, SeekOrigin.Begin);
			using (StreamReader reader = new StreamReader(stream, encoding))
			{
				return reader.ReadToEnd();
			}
		}
	}
}