concatWithSingleList method
Returns a list that concatenates this iterable with iterable.
If either iterable is empty, the result contains the elements of the other iterable.
Implementation
List<E> concatWithSingleList(Iterable<E> iterable) {
if (iterable.isEmpty) return toList();
if (isEmpty) return iterable.toList();
return <E>[...this, ...iterable];
}