visitContentsAsFileTrees(child -> child.visit(visitor));
        return this;
    }

    @Override
    public void visitContentsAsFileTrees(Consumer<FileTreeInternal> visitor) {
        visitContents(new FileCollectionStructureVisitor() {
            @Override
            public void visitCollection(Source source, Iterable<File> contents) {
                throw new UnsupportedOperationException("Should not be called");

    public String getDisplayName() {
        return displayName;
    }

    @Override
    public Set<File> getFiles() {
        return ImmutableSet.of();
    }

    @Override
    protected void visitContents(FileCollectionStructureVisitor visitor) {
    }

    @Override
    public FileTreeInternal getAsFileTree() {
        return new EmptyFileTree(FileTreeInternal.DEFAULT_TREE_DISPLAY_NAME);
    }

    @Override