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();
    }