How to use the oscrypto._ffi.null function in oscrypto

sec_transform = None

    try:
        cf_dict = CFHelpers.cf_dictionary_from_pairs([(Security.kSecAttrKeyType, cipher)])
        cf_key = CFHelpers.cf_data_from_bytes(key)
        cf_data = CFHelpers.cf_data_from_bytes(data)

        error_pointer = new(CoreFoundation, 'CFErrorRef *')
        sec_key = Security.SecKeyCreateFromData(cf_dict, cf_key, error_pointer)
        handle_cf_error(error_pointer)

        sec_transform = Security.SecEncryptTransformCreate(sec_key, error_pointer)
        handle_cf_error(error_pointer)

        if cipher != Security.kSecAttrKeyTypeRC4:
            Security.SecTransformSetAttribute(sec_transform, Security.kSecModeCBCKey, null(), error_pointer)
            handle_cf_error(error_pointer)

            Security.SecTransformSetAttribute(sec_transform, Security.kSecPaddingKey, padding, error_pointer)
            handle_cf_error(error_pointer)

            cf_iv = CFHelpers.cf_data_from_bytes(iv)
            Security.SecTransformSetAttribute(sec_transform, Security.kSecIVKey, cf_iv, error_pointer)
            handle_cf_error(error_pointer)

        Security.SecTransformSetAttribute(
            sec_transform,
            Security.kSecTransformInputAttributeName,
            cf_data,
            error_pointer
        )
        handle_cf_error(error_pointer)

if is_null(stack_pointer):
            handle_openssl_error(0, TLSError)

        if libcrypto_version_info < (1, 1):
            number_certs = libssl.sk_num(stack_pointer)
        else:
            number_certs = libssl.OPENSSL_sk_num(stack_pointer)

        self._intermediates = []

        for index in range(0, number_certs):
            if libcrypto_version_info < (1, 1):
                x509_ = libssl.sk_value(stack_pointer, index)
            else:
                x509_ = libssl.OPENSSL_sk_value(stack_pointer, index)
            buffer_size = libcrypto.i2d_X509(x509_, null())
            cert_buffer = buffer_from_bytes(buffer_size)
            cert_pointer = buffer_pointer(cert_buffer)
            cert_length = libcrypto.i2d_X509(x509_, cert_pointer)
            handle_openssl_error(cert_length)
            cert_data = bytes_from_buffer(cert_buffer, cert_length)

            cert = Asn1Certificate.load(cert_data)

            if index == 0:
                self._certificate = cert
            else:
                self._intermediates.append(cert)

schannel_cred.dwMaximumCipherStrength = 0
        # Default session lifetime is 10 hours
        schannel_cred.dwSessionLifespan = 0
        schannel_cred.dwFlags = flags
        schannel_cred.dwCredFormat = 0

        cred_handle_pointer = new(secur32, 'CredHandle *')

        result = secur32.AcquireCredentialsHandleW(
            null(),
            Secur32Const.UNISP_NAME,
            Secur32Const.SECPKG_CRED_OUTBOUND,
            null(),
            schannel_cred_pointer,
            null(),
            null(),
            cred_handle_pointer,
            null()
        )
        handle_error(result)

        self._credentials_handle = cred_handle_pointer

if iv is None:
            iv_len = 0
        else:
            iv_len = len(iv)

        flags = 0
        if padding is True:
            flags = BcryptConst.BCRYPT_BLOCK_PADDING

        out_len = new(bcrypt, 'ULONG *')
        res = bcrypt.BCryptEncrypt(
            key_handle,
            data,
            len(data),
            null(),
            null(),
            0,
            null(),
            0,
            out_len,
            flags
        )
        handle_error(res)

        buffer_len = deref(out_len)
        buffer = buffer_from_bytes(buffer_len)
        iv_buffer = buffer_from_bytes(iv) if iv else null()

        res = bcrypt.BCryptEncrypt(
            key_handle,
            data,

handshake_server_bytes += bytes_read
                self._received_bytes += bytes_read

                in_buffers[0].cbBuffer = len(self._received_bytes)
                write_to_buffer(in_data_buffer, self._received_bytes)

                result = secur32.InitializeSecurityContextW(
                    self._session._credentials_handle,
                    temp_context_handle_pointer,
                    self._hostname,
                    self._context_flags,
                    0,
                    0,
                    in_sec_buffer_desc_pointer,
                    0,
                    null(),
                    out_sec_buffer_desc_pointer,
                    output_context_flags_pointer,
                    null()
                )

                if result == Secur32Const.SEC_E_INCOMPLETE_MESSAGE:
                    in_buffers[0].BufferType = Secur32Const.SECBUFFER_TOKEN
                    # Windows 10 seems to fill the second input buffer with
                    # a BufferType of SECBUFFER_MISSING (4), which if not
                    # cleared causes the handshake to fail.
                    if in_buffers[1].BufferType != Secur32Const.SECBUFFER_EMPTY:
                        in_buffers[1].BufferType = Secur32Const.SECBUFFER_EMPTY
                        in_buffers[1].cbBuffer = 0
                        if not is_null(in_buffers[1].pvBuffer):
                            secur32.FreeContextBuffer(in_buffers[1].pvBuffer)
                            in_buffers[1].pvBuffer = null()

if certificate_or_public_key.algorithm == 'rsa':
        if rsa_pss_padding:
            flags = BcryptConst.BCRYPT_PAD_PSS
            padding_info_struct_pointer = struct(bcrypt, 'BCRYPT_PSS_PADDING_INFO')
            padding_info_struct = unwrap(padding_info_struct_pointer)
            # This has to be assigned to a variable to prevent cffi from gc'ing it
            hash_buffer = buffer_from_unicode(hash_constant)
            padding_info_struct.pszAlgId = cast(bcrypt, 'wchar_t *', hash_buffer)
            padding_info_struct.cbSalt = len(digest)
        else:
            flags = BcryptConst.BCRYPT_PAD_PKCS1
            padding_info_struct_pointer = struct(bcrypt, 'BCRYPT_PKCS1_PADDING_INFO')
            padding_info_struct = unwrap(padding_info_struct_pointer)
            # This has to be assigned to a variable to prevent cffi from gc'ing it
            if hash_algorithm == 'raw':
                padding_info_struct.pszAlgId = null()
            else:
                hash_buffer = buffer_from_unicode(hash_constant)
                padding_info_struct.pszAlgId = cast(bcrypt, 'wchar_t *', hash_buffer)
        padding_info = cast(bcrypt, 'void *', padding_info_struct_pointer)
    else:
        # Windows doesn't use the ASN.1 Sequence for DSA/ECDSA signatures,
        # so we have to convert it here for the verification to work
        try:
            signature = DSASignature.load(signature).to_p1363()
        except (ValueError, OverflowError, TypeError):
            raise SignatureError('Signature is invalid')

    res = bcrypt.BCryptVerifySignature(
        certificate_or_public_key.key_handle,
        padding_info,
        digest,

format_pointer = new(Security, 'uint32_t *')
        pointer_set(format_pointer, SecurityConst.kSecFormatOpenSSL)
        type_pointer = new(Security, 'uint32_t *')
        pointer_set(type_pointer, item_type)
        keys_pointer = new(CoreFoundation, 'CFArrayRef *')

        attr_array = CFHelpers.cf_array_from_list([
            Security.kSecAttrIsExtractable
        ])

        import_export_params_pointer = new(Security, 'SecItemImportExportKeyParameters *')
        import_export_params = unwrap(import_export_params_pointer)
        import_export_params.version = 0
        import_export_params.flags = 0
        import_export_params.passphrase = null()
        import_export_params.alertTitle = null()
        import_export_params.alertPrompt = null()
        import_export_params.accessRef = null()
        import_export_params.keyUsage = null()
        import_export_params.keyAttributes = attr_array

        res = Security.SecItemImport(
            cf_source,
            null(),
            format_pointer,
            type_pointer,
            0,
            import_export_params_pointer,
            null(),
            keys_pointer
        )
        handle_sec_error(res)

def _load_x509(certificate):
    """
    Loads an ASN.1 object of an x509 certificate into a Certificate object

    :param certificate:
        An asn1crypto.x509.Certificate object

    :return:
        A Certificate object
    """

    source = certificate.dump()

    buffer = buffer_from_bytes(source)
    evp_pkey = libcrypto.d2i_X509(null(), buffer_pointer(buffer), len(source))
    if is_null(evp_pkey):
        handle_openssl_error(0)
    return Certificate(evp_pkey, certificate)