I want to bind items width and height to a model.

For some items width and height is specified but most of them should be set to "Auto" mode.

So i created model with property:

```
    public double? Height
    {
        get
        {
            return this.height;
        }

        set
        {
            this.height = value;
            this.OnPropertyChanged("Height");
        }
    }

```

And i bind it to my view. 

In case if **height == null** my control size is set to auto and this is OK.
But i have exceptions:

```
    System.Windows.Data Error: 5 : Value produced by BindingExpression is not valid for target property.; Value='<null>' BindingExpression:Path=Height;
target property is 'Height' (type 'Double')

```

How can i force my control to set height to 'Auto' and avoid exceptions generation?