public Node parse() throws ScanException {
    if (tokenList == null || tokenList.isEmpty())
      return null;
    return E();
  }
@Test
  public void withDefault() throws ScanException {
    Tokenizer tokenizer = new Tokenizer("${b:-c}");
    Parser parser = new Parser(tokenizer.tokenize());
    Node node = parser.parse();
    Node witness = new Node(Node.Type.VARIABLE, new Node(Node.Type.LITERAL, "b"));
    witness.defaultPart = new Node(Node.Type.LITERAL, "c");
    assertEquals(witness, node);
  }