Web API Restful service ReadAsAsync<type> not returning lists

Question

I am trying to return lists of objects inside of a class, however when I try to read the result into the container class it nulls out the lists. I am pretty new to Web API so I don't know if this is by design or if I am doing something wrong. If I read the response content into a string the lists are there. The first image shows that the lists are intact and the second shows that they are no longer available. Any direction would be appreciated!

 using (HttpClient client = new HttpClient())
            {
                string url = Url(String.Format("{0}", id));
                SetupClient(client, url);

                HttpResponseMessage response = client.GetAsync(url).Result;

                if (response.IsSuccessStatusCode)
                {


                    shipment = response.Content.ReadAsAsync<ShipmentViewModel>().Result;

                }

Edit for adding ShipmentViewModel source

public class ShipmentViewModel
{
    public Guid Id { get; set; }

    public String ShipmentName { get; set; }

    public String Description { get; set; }

    public String Comments { get; set; }

    /// <summary>
    /// Used for UI display purposes only
    /// </summary>

    public int NumberOrdersScanned { get; set; }
    public int NumberOrdersTotal { get; set; }

    public int NumberParcelsScanned { get; set; }
    public int NumberParcelsTotal { get; set; }

    public List<ShipmentEntity> ShipmentEntities { get; set; }

    public ShipmentEntity ShipmentEntity { get; set; }
    public Guid ValidationTypeId { get; set; }
    //        public string ValidationType { get; set; }
    public ValidationType ValidationType { get; set; }
    public List<ValidationType> ValidationTypes { get; set; }
    /// <summary>
    /// Used for UI display purposes only
    /// </summary>
    public List<ShipmentStatus> ShipmentStatuses { get; set; }

    public ShipmentStatus ShipmentStatus { get; set; }

    /// <summary>
    /// Used for UI display purposes only
    /// </summary>
    public List<ShipmentDestinationCountry> DestinationCountries { get; set; }

    public ShipmentDestinationCountry DestinationCountry { get; set; }

    private List<ShipmentTrackingNumber> _TrackingNumbers;
    public List<ShipmentTrackingNumber> TrackingNumbers
    {
        get
        {
            return _TrackingNumbers ?? (_TrackingNumbers = new List<ShipmentTrackingNumber>());
        }
        set
        {
            _TrackingNumbers = value;
        }
    }

    public bool RequiresValidation { get; set; }
    private List<ShipmentValidationViewModel> _Validations { get; set; }

    public List<ShipmentValidationViewModel> Validations
    {
        get
        {
            return _Validations ?? (_Validations = new List<ShipmentValidationViewModel>());
        }
        set
        {
            _Validations = value;
        }
    }

    public Guid EdiShipmentInfoId { get; set; }
    public EdiShipmentInfoViewModel EdiShipmentInfo { get; set; }

    public ShipmentEvents Events { get; set; }
}

Here is the EdiShipmentInfoViewModel

 public class EdiShipmentInfoViewModel
{
    //        private string _packagingCode;
    public Guid Id { get; set; }
    public Guid ShipmentId { get; set; }
    public Guid WarehouseId { get; set; }
    public virtual InternalLookupModel Warehouse { get; set; }
    public DateTime? ShippingDate { get; set; }
    public DateTime? DeliveryDate { get; set; }
    public string EquipmentNumber { get; set; }

    public string ShippingWeight { get; set; }

    public string PackagingCode { get; set; }

    public string CarrierCommonName { get; set; }
    public Guid ScacCodeId { get; set; }
    public virtual InternalLookupModel ScacCode { get; set; }
    public Guid PackagingFormId { get; set; }
    public virtual InternalLookupModel PackagingForm { get; set; }
    public Guid PackagingMaterialId { get; set; }
    public virtual InternalLookupModel PackagingMaterial { get; set; }

    public string MasterBillLading { get; set; }
    public string BillLading { get; set; }
    public string LadingDescription { get; set; }
    public string FobShippingPoint { get; set; }
    public string FobDestination { get; set; }
    public Guid TransPayMethodId { get; set; }
    public virtual InternalLookupModel TransPayMethod { get; set; }
    public Guid TransTypeId { get; set; }
    public virtual InternalLookupModel TransType { get; set; }
    public Guid ServiceLevelCodeId { get; set; }
    public virtual InternalLookupModel ServiceLevelCode { get; set; }
    public Guid UnitOfMeasureId { get; set; }
    public virtual InternalLookupModel UnitOfMeasure { get; set; }


    private List<InternalLookupModel> _WarehouseList;
    public List<InternalLookupModel> WarehouseList
    {
        get { return _WarehouseList ?? new List<InternalLookupModel>(); }
        set { this._WarehouseList = value; }
    }

    private List<InternalLookupModel> _ScacCodeList;

    public List<InternalLookupModel> ScacCodeList
    {
        get { return _ScacCodeList ?? new List<InternalLookupModel>(); }
        set { this._ScacCodeList = value; }
    }
    private List<InternalLookupModel> _PackagingFormList;
    public List<InternalLookupModel> PackagingFormList
    {
        get { return _PackagingFormList ?? new List<InternalLookupModel>(); }
        set { this._PackagingFormList = value; }
    }

    private List<InternalLookupModel> _PackagingMaterialList;
    public List<InternalLookupModel> PackagingMaterialList
    {
        get { return _PackagingMaterialList ?? new List<InternalLookupModel>(); }
        set { this._PackagingMaterialList = value; }
    }

    private List<InternalLookupModel> _TransPayMethodList;
    public List<InternalLookupModel> TransPayMethodList
    {
        get { return _TransPayMethodList ?? new List<InternalLookupModel>(); }
        set { this._TransPayMethodList = value; }
    }

    private List<InternalLookupModel> _TransTypeList;
    public List<InternalLookupModel> TransTypeList
    {
        get { return _TransTypeList ?? new List<InternalLookupModel>(); }
        set { this._TransTypeList = value; }
    }

    private List<InternalLookupModel> _ServiceLevelCodeList;

    public List<InternalLookupModel> ServiceLevelCodeList
    {
        get { return _ServiceLevelCodeList ?? new List<InternalLookupModel>(); }
        set { this._ServiceLevelCodeList = value; }
    }

    private List<InternalLookupModel> _UnitOfMeasureList;

    public List<InternalLookupModel> UnitOfMeasureList
    {
        get { return _UnitOfMeasureList ?? new List<InternalLookupModel>(); }
        set { this._UnitOfMeasureList = value; }
    }
}

Answer 1

I think @BrianBall is correct. Rewrite your class so that your list properties are simple getters/setters and initialize the lists in your constructor.

public class ShipmentViewModel
{
  public ShipmentViewModel()
  {
    TrackingNumbers = new List<ShipmentTrackingNumber>();
  }

  public List<ShipmentTrackingNumber> TrackingNumbers { get; set; }
  // and so on
}