c# populating view model

I am trying to populate a ViewModel and I am getting an "Object reference not set to an instance of an object." when trying to populate a List within my main view model. See my two ViewModels and my code to populate them.

As you can see I am building a List of InventoryWorkTypesMSViewModel from a common delimited field of WorkTypes in the InventoryViewModel. Am I doing this wrong? If so what should I do to fix it?

public class InventoryViewModel
        public int InventoryId { get; set; }
        public int ProjectId { get; set; }
        public int Qty { get; set; }
        public bool AuditFlag { get; set; }
        public string UpdatedBy { get; set; }
        public DateTime? UpdatedDt { get; set; }
        public int? ProductNameId { get; set; }
        public string Size { get; set; }
        public string WorkTypes { get; set; }
        public List<InventoryWorkTypesMSViewModel> WorkTypesMS { get; set; }

public class InventoryWorkTypesMSViewModel
        public string WorkType { get; set; }

public List<InventoryViewModel> GetList(int projectId, int? productNameId)
                var model = _db.Inventories
                        .Select(i =>
                              new InventoryViewModel
                                  InventoryId = i.InventoryId,
                                  ProjectId = i.ProjectId,
                                  Qty = i.Qty,
                                  AuditFlag = i.AuditFlag,
                                  ProductNameId = i.ProductNameId,
                                  UpdatedBy = i.UpdatedBy,
                                  UpdatedDt = i.UpdatedDt,
                                  Size = i.Size,
                                  WorkTypes = i.WorkTypes

                foreach(var m in model)
                    if(m.WorkTypes != null)
                        string[] workTypeArray = m.WorkTypes.Split(',');

                        foreach(string wt in workTypeArray)
                            m.WorkTypesMS.Add(new InventoryWorkTypesMSViewModel
                                WorkType = wt

                return model;

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Chris StanyonWebDevCommented:
Your WorkTypeMS property is never initiated, so it's null, and you can't add to a null. You should initialise the property before using it:

public List<InventoryWorkTypesMSViewModel> WorkTypesMS { get; set; } = new List<InventoryWorkTypesMSViewModel>();

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deleydSoftware EngineerCommented:
The possible places I see offhand are:
1. Test that the model returned from _db.Inventories isn't null before using it.
2. m.WorkTypesMS.Add(...) can we be assured that m.WorkTypesMS isn't null? (I can't tell from here. It might be OK.)
3. foreach(var m in model) probably OK, probably don't need to check that m is null, unless model is a list which might contain null entries.

Probably likely problem I'll guess is #1.
after var model =
add a line:
if (model == null)
    do something...

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nmiller61Author Commented:
Thanks. I figured it was something simple I missed.
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