Issue with creating weak encryptor

Question

I have this code that I'm trying to use to decrypt some byte array

 public static class DESCryptoExtensions
{
    public static byte[] Encrypt(byte[] data, byte[] key, byte[] IV)
    {
        MemoryStream mStream = new MemoryStream();
        DESCryptoServiceProvider des = new DESCryptoServiceProvider();
        des.Mode = CipherMode.ECB;
        des.Padding = PaddingMode.None;
        CryptoStream cStream = new CryptoStream(mStream,
            des.CreateWeakEncryptor(key, IV),
            CryptoStreamMode.Write);
        cStream.Write(data, 0, data.Length);
        cStream.FlushFinalBlock();
        byte[] ret = mStream.ToArray();
        cStream.Close();
        mStream.Close();
        return ret;
    }

    public static byte[] Decrypt(byte[] data, byte[] key, byte[] IV)
    {
        MemoryStream msDecrypt = new MemoryStream(data);
        DESCryptoServiceProvider des = new DESCryptoServiceProvider();
        des.Mode = CipherMode.ECB;
        des.Padding = PaddingMode.None;
        CryptoStream csDecrypt = new CryptoStream(msDecrypt,
            des.CreateWeakDecryptor(key, IV),
            CryptoStreamMode.Read);
        byte[] fromEncrypt = new byte[data.Length];
        csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length);
        return fromEncrypt;
    }


    #region DESCryptoExtensions
    public static ICryptoTransform CreateWeakEncryptor(this DESCryptoServiceProvider cryptoProvider, byte[] key, byte[] iv)
    {
        MethodInfo mi = cryptoProvider.GetType().GetMethod("_NewEncryptor", BindingFlags.NonPublic | BindingFlags.Instance);
        object[] Par = { key, cryptoProvider.Mode, iv, cryptoProvider.FeedbackSize, 0 };
        ICryptoTransform trans = mi.Invoke(cryptoProvider, Par) as ICryptoTransform;
        return trans;
    }
    public static ICryptoTransform CreateWeakEncryptor(this DESCryptoServiceProvider cryptoProvider)
    {
        return CreateWeakEncryptor(cryptoProvider, cryptoProvider.Key, cryptoProvider.IV);
    }
    public static ICryptoTransform CreateWeakDecryptor(this DESCryptoServiceProvider cryptoProvider, byte[] key, byte[] iv)
    {
        return CreateWeakEncryptor(cryptoProvider, key, iv);
    }
    public static ICryptoTransform CreateWeakDecryptor(this DESCryptoServiceProvider cryptoProvider)
    {
        return CreateWeakDecryptor(cryptoProvider, cryptoProvider.Key, cryptoProvider.IV);
    }
    #endregion
}

Now I try to run this code like so..

   byte[] challenge = new byte[] { 0x93, 0x9d, 0x2c, 0x2e, 0xa1, 0x65, 0x75, 0xd5 };


byte[] rndA = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 };


byte[] key = new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };



var iv = new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };




var test = DESCryptoExtensions.Decrypt(challenge, key, iv);

And then I get an error on this line..

 ICryptoTransform trans = mi.Invoke(cryptoProvider, Par) as ICryptoTransform;

 Object reference not set to an instance of an object.

All I want to do is to decrypt the challenge byte array using the key byte array.. using DES decryption..PLEASE DON'T SUGGEST I CHANGE THE KEY..I've been down a rabbit hole with this stuff so help is appreciated