@Override
  public @NotNull VirtualFile createChildData(Object requestor, @NotNull String name) {
    if (findChild(name) != null) {
      throw new IllegalArgumentException("Child exists: " + name);
    }
    LightVirtualFile file = new AddedVirtualFile(name);
    myAddedChildren.put(name, file);
    return file;
  }
@Override
  public @NotNull VirtualFile createChildData(Object requestor, @NotNull String name)