add method
Adds a resource.
Implementation
void add(String key, Iterable<ContextualResource<T, C>> options) {
if (isEmptyObject(options)) return;
var entries =
_resources.putIfAbsent(key, () => <ContextualResource<T, C>>{});
var size = entries.length;
entries.addAll(options);
if (entries.length != size) {
_resourcesSorted.remove(key);
}
}