then method
Returns a new Comparator combining this one and the given
nextComparator
in the lexicographical order.
Firstly, this comparator will be used, and if the result is 0, the
nextComparator
will be used.
Implementation
Comparator<T> then(Comparator<T> nextComparator) => (a, b) {
final firstComparison = call(a, b);
if (firstComparison == 0) return nextComparator(a, b);
return firstComparison;
};