Error message

• Warning: assert(): Cannot load the "file" entity with NULL ID. failed in Drupal\Core\Entity\EntityStorageBase->load() (line 249 of core/lib/Drupal/Core/Entity/EntityStorageBase.php).
• Warning: array_flip(): Can only flip STRING and INTEGER values! in Drupal\Core\Entity\EntityStorageBase->loadMultiple() (line 266 of core/lib/Drupal/Core/Entity/EntityStorageBase.php).
• Notice: Undefined variable: fileUrl in Drupal\armonea_pricelist\Controller\PriceListIntro->content() (line 96 of modules/custom/armonea_pricelist/src/Controller/PriceListIntro.php).