last(emptyErrorAlternative = THROW_IF_EMPTY) {
        //noinspection JSUnusedAssignment
        let result = EMPTY_SYGIL;
        for (let e of this._iterable) {
            result = e;
        }
        return emptyFallback(result, emptyErrorAlternative, "Empty sequence has no last item.");
    }
Returns the last item in the sequence.
@param {=A} emptyErrorAlternative The value to return if the sequence is empty. If not provided, an error
is thrown when the sequence is empty.
@returns {T|A}
@template T, A