@Override
  public @Nullable String verify(PsiDirectory source) {
    VirtualFile virtualFile = source.getVirtualFile();
    final VirtualFile sourceRootForFile = myFileIndex.getSourceRootForFile(virtualFile);
    if (sourceRootForFile == null) {
      return "";
    }
    if (virtualFile.equals(sourceRootForFile)) return null;
    return checkCanCreateInSourceRoot(sourceRootForFile);
  }
@Override
  public @Nullable String verify(PsiDirectory source)