int mbedtls_asn1_write_null( unsigned char **p, unsigned char *start )
{
    int ret;
    size_t len = 0;

    // Write NULL
    //
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, 0) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_NULL ) );

    return( (int) len );
}
Unknown