Notice: Undefined index: label_attributes

When I try to render a MultiCheckbox element with FormRow view helper:

``` php
$this->formRow($myForm->get('MultiCheckboxElement'));
```

I get the following notice:

> Notice: Undefined index: label_attributes in ../vendor/coremax/core-bootstrap/src/CoreBootstrap/Form/View/Helper/FormRow.php on line 149
