RegisterProperty should support Nullable for lamda expression.

[hoangcuongvn]

Actually the RegisterProperty for lamda expression is like below:

PropertyInfo<P> RegisterProperty<P>(Expression<Func<T, object>> propertyLambdaExpression)

It should be like below:

PropertyInfo<P> RegisterProperty<P>(Expression<Func<T, object?>> propertyLambdaExpression)

Therefore we can declare nullable properties like below without warning:

[Serializable]
class MyClass
{
  public static readonly PropertyInfo<int?> ValProperty = RegisterProperty<int?>(x => x.Val);
  public int? Val
  {
	get { return ReadProperty(ValProperty); }
	set { LoadProperty(VcalProperty, value); }
  }
}

[rockfordlhotka]

@StefanOssendorf , thoughts?