Using a model with a generic type constraint

Question

I'm trying myself at a model that uses a generic type that I constrained with a base class.

I get the following error when calling my view:

The model item passed into the dictionary is of type 'MVCTest.Models.TestModel`1[MVCTest.Models.SpecialColumn]', but this dictionary requires a model item of type 'MVCTest.Models.TestModel`1[MVCTest.Models.ColumnBase]'.

Here is an example code to demonstrate the issue:

public class ColumnBase
{
    public decimal Id { get; set; }
    public string Text { get; set; }
    public bool Enabled { get; set; }

    public ColumnBase()
    {
        Enabled = true;
    }

    public string GetFormattedText(string symbol)
    {
        return string.Format(Text, symbol);
    }
}

public class SpecialColumn : ColumnBase
{
    public string Baz { get; set; }
}

public class TestModel<TColumn>
    where TColumn : ColumnBase
{
    Dictionary<string, TColumn> Columns { get; set; }
}

The Controller:

public ActionResult Test ()
{
    var testModel = new TestModel<SpecialColumn>();

    return View("", testModel);
}

In the view I tried to use ColumnBase as this should be a shared view that just needs the properties provided by ColumnBase:

@model TestModel<ColumnBase>

What is the correct way to implement something like this?