I don't know Rust (though I'm familiar with Java & C) and there's nothing obvious about Box. In fact, I'm just learning from your comment that it means optional.
(Box does not mean optional, the parent is wrong. Option is the type for optional. Box is basically a mallloc, placing a value in the newly allocated memory, and then a call to free automatically when it goes out of scope. The box itself is a pointer to the heap. It’s not allowed to be null, in some sense, the opposite of optional.)
