public boolean add(@NotNull List<VirtualFile> files) {
      for (VirtualFile file : files) {
        if (!myFoundFiles.contains(file)) {
          if (!myExcluded.remove(file)) { //if it was excluded we only delete exclusion mark
            myAdded.add(file);
            myUserAddedToRemove.remove(file);
          }
          else {
            myFoundFiles.add(file);
            return true;
          }
        }
        else {
          myExcluded.remove(file);
        }
      }
      return false;
    }
public boolean add(@NotNull List<VirtualFile> files)