Checkboxlist fall out from parent tag

Hi, I want to customize checkboxes in my checkboxlist, so I set an item template like described here.

When I do that, I get a list of checkboxes and wrapper just after them empty.
If I use basic version:

$weekDays = [
	'monday' => Yii::t('global', 'monday'),
	'tuesday' => Yii::t('global', 'tuesday'),
	'wednesday' => Yii::t('global', 'wednesday'),
	'thursday' => Yii::t('global', 'thursday'),
	'friday' => Yii::t('global', 'friday'),
	'saturday' => Yii::t('global', 'saturday'),
	'sunday' => Yii::t('global', 'sunday'),
];
echo $form->field($model, 'week_days')->checkboxList($weekDays);

The result is fine:

<div class="form-group field-facilityeventform-week_days">
    <label class="control-label">Week Days</label>
    <input type="hidden" name="FacilityEventForm[week_days]" value="">
    <div id="facilityeventform-week_days">
    <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" value="monday" checked=""> monday</label></div>
    <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" value="tuesday"> tuesday</label></div>
    <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" value="wednesday"> wednesday</label></div>
    <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" value="thursday"> thursday</label></div>
    <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" value="friday"> friday</label></div>
    <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" value="saturday"> saturday</label></div>
    <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" value="sunday"> sunday</label></div></div>

    <p class="help-block help-block-error"></p>
    </div>
</div>

But if I set the item template:

echo $form->field($model, 'week_days')->checkboxList($weekDays,
		[
			'item' => function($index, $label, $name, $checked, $value) {
                $checked = $checked ? 'checked' : '';
				echo "<div class=\"checkbox\">
							<label>
								<input type=\"checkbox\" name=\"$name\" $checked value=\"$value\">
								$label
							</label>
						</div>";
			}
		]

Checkboxes get generated outside the parent div:

<form id="facilityEventForm" action="/facility-event/test/" method="post" data-pjax="" autocomplete="off">
        <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" checked="" value="monday">monday</label></div>
        <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" checked="" value="tuesday">tuesday</label></div>
        <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" checked="" value="wednesday">wednesday</label></div>
        <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" checked="" value="thursday">thursday</label></div>
        <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" checked="" value="friday">friday</label></div>
        <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" checked="" value="saturday">saturday</label></div>
        <div class="checkbox"><label><input type="checkbox" name="FacilityEventForm[week_days][]" checked="" value="sunday">sunday</label></div>
        <div class="form-group field-facilityeventform-week_days">
            <label class="control-label">Week Days</label>
            <input type="hidden" name="FacilityEventForm[week_days]" value="">
        <div id="facilityeventform-week_days"></div>
        <p class="help-block help-block-error"></p>
        </div>
        <button type="button" class="btn btn-default" data-dismiss="modal">cancel</button>
        <button type="submit" class="btn btn-primary">save</button>
    </form>

As a result, I get an empty string instead of an array in $_POST.

Tested on clean build - same problem. Both Yii version: 2.0.12

The problem was inside ‘item’ function - there are echo statement, but should be return. Wrote the same message at the source theme of the mistake.