Does not support Select2

I have simple code below and still doesn't support validation.

```
<select class="form-control select2" id="group" required>
  <option value=""></option>
  <option value="1">One</option>
</select>
```
```
<script>
  $('.select2').select2();
  bootstrapValidate("#group", "required:This is required!");
</script>
```
But it worked on input tag.
Any idea?