Why my not-null columns become nullable in my CTE recursive query?

I have a simple hierarchical table. Let's say it has these columns:

Id, [Guid], ParentId, Title

Only ParentId is nullable. Other columns are not nullable.

I have created a recursive query to show me the path from the node up to the root. I have used CTE for this purpose. And this is my query:

with Anchor (Id, [Guid], ParentId, Title, [Path])as(    select Id, [Guid], ParentId, Title, cast('' as nvarchar(100)) as [Path]    from Hierarchies    where ParentId is null    union all    select Hierarchies.Id, Hierarchies.[Guid], Hierarchies.ParentId, Hierarchies.Title, cast(Anchor.[Path] +'/'+ Hierarchies.Title as nvarchar(100)) as [Path]    from Hierarchies    inner join Anchor    on Hierarchies.ParentId = Anchor.Id)select     isnull(Anchor.Id, 0) as Id,    isnull(Anchor.[Guid], newid()) as [Guid],    Anchor.ParentId,    Anchor.Title,    Anchor.[Path]from Anchor

The problem is that, when I turn this query into a view, the Guid column becomes nullable. I even used isnull() function to force it not to be null. And to my surprise, that isnull actually worked for the Id column. But it's not working for Guid.

What should I do? Why SQL Server has this behavior?