Rule source on GitHub

DowngradeNullsafeToTernaryOperatorRector

Change nullsafe operator to ternary operator rector

-$dateAsString = $booking->getStartDate()?->asDateTimeString();
+$dateAsString = ($bookingGetStartDate = $booking->getStartDate()) ? $bookingGetStartDate->asDateTimeString() : null;

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp80\Rector\NullsafeMethodCall\DowngradeNullsafeToTernaryOperatorRector;

return RectorConfig::configure()
    ->withRules([
        DowngradeNullsafeToTernaryOperatorRector::class,
    ]);