Partial View model doesn't resolve

Question

I have a model A which has a property which is of another model type, B. I have a view which is tied to A. I want to add a partial view to to A which takes a model of type B. This is my code

public class ModelA
{
    public bool Prop1 {get;set;}
    public bool Prop2 {get; set;}
    public Dictionary<int, string> Prop3{get; set;}
    public int Prop4 {get; set;}
    public ModelB Prop5 { get; set; }


    public ModelA ()
    {
        Prop5 = null;

       ... more code ...
    }
}

//This view is tied to ModelA
@using (Html.BeginForm("CreateReport", "Home", FormMethod.Post))
{
   some markup
}

//this is the problem
@Html.Partial("FileLinks",  Model.Prop5) //This line throws an error 

Error: The model item passed into the dictionary is of type 'ModelA', but this dictionary requires a model item of type 'ModelB'

The line works if i change it to @Html.Partial("FileLinks", new ModelB())

Why doesn't the original code work? The property is of type ModelB.

Any help is appreciated thanks!

Update: I forgot to add some code from the Controller

m.FileLinks = new ModelB() return View("Index", m)

So the model is not null

Answer 1

what i think happening here is that

when you render a partial view like this the ViewDataDictionary and the Views Context is passed to the partial view
so when the ModelB is null then the ViewDataDictionary<TModel> isnt changed and at runtime teh MVC engine cannot determine the type of model from a null value.