ariya/esprima — pull request #241 by zxqfox (2014-04-04 22:59:58+00:00)
Title: introduce EmptyExpression instead of null for [,,]

required for mdevils/node-jscs/issues/315
null don't have any information about where the token was.
for example:
```js
var x = [
, 4,
,
];
```

WARN: I'm not sure about lookahead, is it right to use it there in parseEmptyExpression?