Error in `BaseHtml::addCssClass()`

[WinterSilence]

What steps will reproduce the problem?

Pass as array:

$options = ['class' => ['form-control-sm']];
Html::addCssClass($options, ['widget' => 'form-control']);
Html::addCssClass($options, ['widget' => 'form-control-color']);
echo Html::renderTagAttributes($options);

Pass as string:

$options = ['class' => 'form-control-sm'];
Html::addCssClass($options, ['widget' => 'form-control']);
Html::addCssClass($options, ['widget' => 'form-control-color']);
echo Html::renderTagAttributes($options);

What is the expected result?

Pass as array: class="form-control-sm form-control form-control-color" Pass as string: class="form-control-sm form-control form-control-color"

What do you get instead?

Pass as array: class="form-control-sm form-control" Pass as string: class="form-control-sm form-control form-control-color"

Additional info

Q	A
Yii version	2.0.44
PHP version	any
Operating system	any

[samdark]

Looks like a bug to me. @yiisoft/reviewers do you remember if such behavior was used anywhere?