✅ Nullable DateTimeOffset field in a [FromForm] model is always null

public class UpdateSelfRequest
{
    public string NationalId { get; set; } = string.Empty;
    public string? Phone { get; set; }
    public string? Address { get; set; }
    public DateTimeOffset? BirthDate { get; set; }
    public IFormFile? Image { get; set; }
}

[HttpPut("UpdateSelf/{NationalId}")]
[Authorize(Roles = AuthRoles.Employee)]
[Consumes("multipart/form-data")]
public async Task<IActionResult> UpdateSelf(
    [FromRoute] string NationalId,
    [FromForm] UpdateSelfRequest req)
{
    // -----> Here, req.BirthDate is null despite the client sending a value
    var result = await _service.UpdateSelf(NationalId, req);
    if (!result.Success)
    {
            return Forbid();
    }

    return Ok();
}