c#. Рутокен 3.0. Ubuntu 20 Value cannot be null. (Parameter 'source')

        public List<(ObjectHandle cert, ObjectHandle key)> GetCertAndKey(Session Session, string CkaId)
        {
            List<(ObjectHandle cert, ObjectHandle key)> res = new();

            List<CKA> CKAAttributes = new List<CKA> { CKA.CKA_ID, CKA.CKA_CLASS, CKA.CKA_LABEL, CKA.CKA_PRIVATE };

            var certificates = Session.FindAllObjects(CertificateAttributes);               // Получить массив хэндлов сертификатов

            foreach (var cert in certificates)
            {
                var attr = Session.GetAttributeValue(cert, CKAAttributes);

                byte[] ar = attr[0].GetValueAsByteArray();

                string cka = BitConverter.ToString(ar);

                if (cka == CkaId)
                {
                    var keys = Session.FindAllObjects(PrivateKeyAttributes);               // Получить массив хэндлов приватных ключей

                    foreach (var key in keys)
                    {
                        var attr2 = Session.GetAttributeValue(key, CKAAttributes);

                        byte[] ar2 = attr[0].GetValueAsByteArray();

                        string cka2 = BitConverter.ToString(ar2);

                        if (cka2 == CkaId)
                        {
                            res.Add((cert, key));

                            break;
                        }
                    }

                    break;
                }
            }

            return res;
        }

var pairs = GetCertAndKey(session, _ckaId);  

if (pairs == null)
{
   throw new Exception($"Не найден сертификат или приватный ключ по указанному id: {_ckaId}");
}

byte[] ar = File.ReadAllBytes(FilePath);

                       
return session.PKCS7Sign(ar, pairs[0].cert, pairs[0].key, null, SampleConstants.UseHardwareHash);      

    public static byte[] PKCS7Sign(this Net.Pkcs11Interop.HighLevelAPI.Session session, byte[] data, Net.Pkcs11Interop.HighLevelAPI.ObjectHandle certificate, Net.Pkcs11Interop.HighLevelAPI.ObjectHandle privateKey, uint[] certificates, uint flags)
    {
        if (Platform.UnmanagedLongSize == 4)
        {
            if (Platform.StructPackingSize == 0)
            {
                Net.Pkcs11Interop.HighLevelAPI40.ObjectHandle certificate2 = new Net.Pkcs11Interop.HighLevelAPI40.ObjectHandle((uint)certificate.ObjectId);
                Net.Pkcs11Interop.HighLevelAPI40.ObjectHandle privateKey2 = new Net.Pkcs11Interop.HighLevelAPI40.ObjectHandle((uint)privateKey.ObjectId);
                return session.HLA40Session.PKCS7Sign(data, certificate2, privateKey2, certificates, flags);
            }

            Net.Pkcs11Interop.HighLevelAPI41.ObjectHandle certificate3 = new Net.Pkcs11Interop.HighLevelAPI41.ObjectHandle((uint)certificate.ObjectId);
            Net.Pkcs11Interop.HighLevelAPI41.ObjectHandle privateKey3 = new Net.Pkcs11Interop.HighLevelAPI41.ObjectHandle((uint)privateKey.ObjectId);
            return session.HLA41Session.PKCS7Sign(data, certificate3, privateKey3, certificates, flags);
        }

        if (Platform.StructPackingSize == 0)
        {
            Net.Pkcs11Interop.HighLevelAPI80.ObjectHandle certificate4 = new Net.Pkcs11Interop.HighLevelAPI80.ObjectHandle((uint)certificate.ObjectId);
            Net.Pkcs11Interop.HighLevelAPI80.ObjectHandle privateKey4 = new Net.Pkcs11Interop.HighLevelAPI80.ObjectHandle((uint)privateKey.ObjectId);
            ulong[] certificates2 = ((IEnumerable<uint>)certificates).Select((Func<uint, ulong>)((uint cert) => cert)).ToArray();
            return session.HLA80Session.PKCS7Sign(data, certificate4, privateKey4, certificates2, flags);
        }

        Net.Pkcs11Interop.HighLevelAPI81.ObjectHandle certificate5 = new Net.Pkcs11Interop.HighLevelAPI81.ObjectHandle((uint)certificate.ObjectId);
        Net.Pkcs11Interop.HighLevelAPI81.ObjectHandle privateKey5 = new Net.Pkcs11Interop.HighLevelAPI81.ObjectHandle((uint)privateKey.ObjectId);
        ulong[] certificates3 = ((IEnumerable<uint>)certificates).Select((Func<uint, ulong>)((uint cert) => cert)).ToArray();
        return session.HLA81Session.PKCS7Sign(data, certificate5, privateKey5, certificates3, flags);
    }