Object item is removed by `flatten()`. 

Here is the problem.

```javascript
var a = [{a:1},{b:1}];
System.println(a);
System.println(a.flatten());
```

The result is as follows.

```
[{"a":1}, {"b":1}]
{}
```

Expectation is below.

```
[{"a":1}, {"b":1}]
[{"a":1}, {"b":1}]
```
