A singleton used to indicate that a late Member of a particular instance has not been initialized.

For example, given

class Example() {
    shared late Example parent;
}

Then

value ex = Example();// uninitialized parent
value context = serialization();
value refs = context.references(ex);
assert(is Member parentRef = refs.find((element) => element is Member));
assert(parentRef.referred(ex) == uninitializedLateValue);

Thus, if a serialization library supports it, it is possible to serialize uninitialized late values.