public int getMessageCount(@Nullable CompilerMessageCategory category) {
    if (category != null) {
      Collection<CompilerMessage> collection = myMessages.get(category);
      return collection != null ? collection.size() : 0;
    }
    return myMessages.values().stream().filter(Objects::nonNull).mapToInt(Collection::size).sum();
  }
public int getMessageCount(@Nullable CompilerMessageCategory category)