Example that breaks `GridFieldConfig_RelationEditor`

Dummy.php

<?php

use SilverStripe\ORM\DataObject;

class Dummy extends DataObject {

    private static $db = [
        'Title' => 'Varchar',
    ];

    private static $many_many = [
        'SubDummies' => SubDummy::class
    ];
    private static $table_name = 'Dummy';
}

DummyAdmin.php

<?php

use SilverStripe\Admin\ModelAdmin;

class DummyAdmin extends ModelAdmin {

    private static $url_segment = 'dummy';

    private static $managed_models = [
        Dummy::class,
        SubDummy::class,
    ];

}

SubDummy.php

<?php
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Filters\PartialMatchFilter;


class SubDummy extends DataObject {

    private static $db = [
        'Title' => 'Varchar',
        'Category' => 'Varchar',
    ];

    private static $belongs_many_many = [
        'Dummies' => Dummy::class
    ];

    private static $table_name = 'SubDummy';

    private static $searchable_fields = [
        'Title' => [
            'title' => 'Title (partial)',
            'filter' => PartialMatchFilter::class,
        ]
    ];
}