Call to a member function isRelation() on null

Hello. Trying to create select option getting such error on field "subuser_id". Thanks for any help
https://gist.github.com/antonbelov/ddbfe416bcf0cd132393c38e8d09c933

->createOptionForm(function (Form $form) {
        return SubuserResource::form($form);
    })

->createOptionForm(function (Form $form) {
        return SubuserResource::form($form);
    })

does not help. Same error

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