Collapse: If content is not an array, footer gets ignored

[Commifreak]

What steps will reproduce the problem?

Create a Collapse widget with non-array content and set footer

			$items[] = [
			        'label' =>      'Label',
			        'content' => 'Test',
                    'footer' => 'Footer'
			        ];

What's expected?

Display content as-is along with the specified footer

What do you get instead?

Footer only gets displayed, when content is an array: https://github.com/yiisoft/yii2-bootstrap/blob/master/src/Collapse.php#L227

Additional info

Q	A
Yii-Bootstrap vesion	2.0.11
Yii vesion	2.0.43
PHP version	7.4
Operating system	Linux

[Commifreak]

The change came with: 599d60c - before that, footer seemed unsupported.

Maybe footer could be supported for both variants, regardles of content's type?