private @NotNull Object2IntMap<String> getValueStamps(String context) {
    return myValueStamps.computeIfAbsent(context, __ -> {
      Object2IntMap<String> result = new Object2IntOpenHashMap<>();
      result.defaultReturnValue(-1);
      return result;
    });
  }
private @NotNull Object2IntMap<String> getValueStamps(String context)