public static <T> void add(@NotNull Map<? super T, IntSet> targetMap, @NotNull T key, int value) {
    IntSet set = targetMap.computeIfAbsent(key, __ -> new IntOpenHashSet());
    set.add(value);
  }
public static <T> void add(@NotNull Map<? super T, IntSet> targetMap, @NotNull T key, int value)