> it's such a joy when you define a variable of type Foo and know it won't contain null

Why is that? I've never seen a good explanation of this point of view.

This all feels like just syntactic sugar to me. Sure you might not have null, you might have an empty object or any other variation. At the end of the day, if a value was expected to be available but is not available (for whatever reason), reliable code is going to have to deal with that absence. No matter how it is expressed.