In versions before 0.2.1, SinglyLinkedList::remove is safe and walks the intrusive list with an unchecked dereference. On an empty list, or when node is not in the list, (*current elm).next reads a null pointer. That is undefined behavior. The list head is a raw *mut Node<T>, and safe code can construct the empty list.

The maintainer fixed this in 0.2.1 by rejecting those two cases with an unconditional assert! before the pointer is followed, matching the upstream Zig unwrap on the same paths. 0.2.0 was yanked. Versions 0.1.0 through 0.1.13 are still published and still contain the unchecked walk.