Error: Call to a member function append() on null in Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\PSR4::toPSR4() (line 54 of [error]
/var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/src/Plugin/DMU/Converter/PSR4.php) #0
/var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/src/Plugin/DMU/Converter/PSR4.php(34):
Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\PSR4::toPSR4()
#1 [internal function]: Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\PSR4->Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\{closure}()
#2 /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/vendor/jcnventura/pharborist/src/NodeCollection.php(669): array_walk()
#3 /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/src/Plugin/DMU/Converter/PSR4.php(35): Pharborist\NodeCollection->each()
#4 /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/drupalmoduleupgrader.drush.inc(352):
Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\PSR4->convert()
#5 /opt/drush-8.x/vendor/drush/drush/includes/command.inc(422): drush_drupalmoduleupgrader_dmu_upgrade()
#6 /opt/drush-8.x/vendor/drush/drush/includes/command.inc(231): _drush_invoke_hooks()
#7 /opt/drush-8.x/vendor/drush/drush/includes/command.inc(199): drush_command()
#8 /opt/drush-8.x/vendor/drush/drush/lib/Drush/Boot/BaseBoot.php(67): drush_dispatch()
#9 /opt/drush-8.x/vendor/drush/drush/includes/preflight.inc(67): Drush\Boot\BaseBoot->bootstrap_and_dispatch()
#10 /opt/drush-8.x/vendor/drush/drush/drush.php(12): drush_main()
#11 {main}.
Error: Call to a member function append() on null in /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/src/Plugin/DMU/Converter/PSR4.php on line 54 #0 /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/src/Plugin/DMU/Converter/PSR4.php(34): Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\PSR4::toPSR4()
#1 [internal function]: Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\PSR4->Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\{closure}()
#2 /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/vendor/jcnventura/pharborist/src/NodeCollection.php(669): array_walk()
#3 /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/src/Plugin/DMU/Converter/PSR4.php(35): Pharborist\NodeCollection->each()
#4 /var/www/html/vhost/drupal9/web/modules/contrib/drupalmoduleupgrader/drupalmoduleupgrader.drush.inc(352): Drupal\drupalmoduleupgrader\Plugin\DMU\Converter\PSR4->convert()