Partial property for default value?

I'd like to 
```csharp
    [Reactive]
    public partial string Title { get; set; } = string.Empty;

// or
    [Reactive(InitialValue = "Default Value")]
    public partial string Title { get; set; }
```

Now I get warning  `_title Non-nullable variable must contain a non-null value when exiting constructor. Consider declaring it as nullable.`