TYPO3 Core

I got a little Problem with the Request Class of Typo3.

I have to use ID ´s from an Api to generate input fields for a fluid form.
The Problem here is:

public function setArgument($argumentName, $value)
    {
        if (!is_string($argumentName) || $argumentName === '') {
            throw new \TYPO3\CMS\Extbase\Mvc\Exception\InvalidArgumentNameException('Invalid argument name.', 1210858767);
        }
        if ($argumentName[0] === '_' && $argumentName[1] === '_') {
            $this->internalArguments[$argumentName] = $value;
            return;
        }
        if (!in_array($argumentName, ['@extension', '@subpackage', '@controller', '@action', '@format', '@vendor'], true)) {
            $this->arguments[$argumentName] = $value;
        }
    }

!is_string let me get an error all the time.

 <label for="{question.id}">{question.label}</label>
 <f:form.textfield class="form-control" name="{question.id}" additionalAttributes="{required: 'required'}"/>

The Problem is, that I have to send the inputs back to the Api, thats why I need the Id.
It´s also a problem that I dont know how many or what type of inputs coming from the API. It could be one, it could be 20...
Is there a solution for this? I dont want to change something in the core-code. And XClasses doenst work here right?

Best Regards,
Benjamin

Patch set 1 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/66215