FulltextSearchable::enable(); throw error in InheritanceMiddleware

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Silverstripe Version: 4.8.0

Question:

Hello when i try to enable FulltextSearchable according to documentation i got error

Uncaught TypeError: Argument 1 passed to SilverStripe\Config\MergeStrategy\Priority::mergeArray() must be of the type array, string given, called in /var/webpage/cms/vendor/silverstripe/framework/src/Core/Config/Middleware/InheritanceMiddleware.php on line 43

my _config.php

use SilverStripe\ORM\Search\FulltextSearchable;

FulltextSearchable::enable();

How can i deal with it?

    public function getClassConfig($class, $excludeMiddleware, $next)
    {
        // Skip if disabled
        var_dump($class);
        $config = $next($class, $excludeMiddleware);
        if (!$this->enabled($excludeMiddleware)) {
            return $config;
        }

        // Skip if not a class or not parent class
        $parent = class_exists($class) ? get_parent_class($class) : null;
        if (!$parent) {
            return $config;
        }

        // Merge with parent class
        $parentConfig = Config::inst()->get($parent, null, $excludeMiddleware);
        return Priority::mergeArray($config, $parentConfig);
    }

I checked that class passed to this function is

SilverStripe\ORM\Search\FulltextSearchable

But $config is empty for this class how can i solve this problem?