Error from version 1.6.0 with PHP 5.6

[yuryeuceda]

Friend

I'm using PHP 5.6 and I update the active form widget with composer and I got 1.6.1 version and then I was having an error with ?? operator in file ActiveForm.php
I did some research and I found that operator ?? doesn't exist in PHP 5.6. So I downgrade the version to 1.5.9 and it works like a charm. (BTW I can't upgrade PHP from 5.6 to 7 due to company policies)

The problem is lines 216 and 217 as shown in picture

I would like if is possible to revert this change in order to keep compatibility with the widget for PHP 5.6 projects.

Thank you very much for your effort.

[kartik-v]

Noting an enhancement for backward compatibility - its difficult though for future... as Yii framework itself is moving to PHP 7.x and beyond.