Fatal error ComputedItemListTrait class

steps
convert from php 5.6.32 to 7.2.0
attempt to edit a book page content node

expectation
no errors

what happened
Fatal error: Declaration of Drupal\Core\TypedData\ComputedItemListTrait::getValue() must be compatible with Drupal\Core\Field\FieldItemList::getValue($include_computed = false) in /var/www/html/webdata/drupal843/core/modules/path/src/Plugin/Field/FieldType/PathFieldItemList.php on line 13

OS Fedora 25 server
webserver apache 2.4.27
PHP version 7.2.0 ,
Drupal version 8.4.3

solution
revert to 5.6.32 -- but its a bad move. going backwards is not progress