Country Dropdown For Custom Product Attribute does not work

I am trying to create a country dropdown for a custom product attribute.

This is the error message:

Error: Call to undefined method
MagentoDirectoryModelConfigSourceCountry::setAttribute() in
/var/www/html/vendor/magento/module-eav/Model/Entity/Attribute/AbstractAttribute.php:652

This is my install:

$eavSetup->addAttribute(
            MagentoCatalogModelProduct::ENTITY,
            'countries',
            [
                'group' => 'Countries',
                'type' => 'text',
                'frontend' => '',
                'label' => 'Countries',
                'input' => 'multiselect',
                'class' => '',
                'source' => 'MagentoDirectoryModelConfigSourceCountry',
                'backend' => 'MagentoEavModelEntityAttributeBackendArrayBackend',
                'global' => MagentoEavModelEntityAttributeScopedAttributeInterface::SCOPE_GLOBAL,
                'visible' => true,
                'required' => false,
                'user_defined' => false,
                'default' => '',
                'searchable' => false,
                'filterable' => false,
                'comparable' => false,
                'visible_on_front' => false,
                'used_in_product_listing' => false,
                'unique' => false,
                'apply_to' => 'configurable',
            ]
        );

The issue is with the source:

'source' => 'MagentoDirectoryModelConfigSourceCountry',