#PHPStan-Strict

Every content entity type extending ContentEntityBase will have an integer ID field (see baseFieldDefinitions), so only content entity type classes that do not extend that base class could implement string IDs.

    $fields = parent::baseFieldDefinitions($entity_type);
    // In order to work around the InnoDB 191 character limit on utf8mb4
    // primary keys, we set the character set for the field to ASCII.
    $fields['id'] = BaseFieldDefinition::create('string')
      ->setLabel(new TranslatableMarkup('ID'))
      ->setReadOnly(TRUE)
      ->setSetting('is_ascii', TRUE);