@Override
  public @Nullable VirtualFileEnumeration extractFileEnumeration() {
    VirtualFileEnumeration enumeration = myVirtualFileEnumeration;
    long currentVFSStamp = VirtualFileManager.VFS_STRUCTURE_MODIFICATIONS.getModificationCount();
    if (currentVFSStamp != myVFSModificationCount) {
      myVirtualFileEnumeration = enumeration = doExtractFileEnumeration();
      myVFSModificationCount = currentVFSStamp;
    }
    return enumeration == VirtualFileEnumeration.EMPTY ? null : enumeration;
  }
@Override
  public @Nullable VirtualFileEnumeration extractFileEnumeration()