public Node parse() throws ScanException {
    if (tokenList == null || tokenList.isEmpty())
      return null;
    return E();
  }
@Test
  public void emptyTokenListDoesNotThrowNullPointerException() throws ScanException {
    // An empty token list would be returned from Tokenizer.tokenize()
    // if it were constructed with an empty string. The parser should
    // be able to handle this.
    Parser parser = new Parser(new ArrayList<Token>());
    parser.parse();
  }