Unable to upload files in SilverStripe 4

Question

I've created a simple extension to SiteConfig to add a logo uploadfield to the settings section. However, the server returns an error upon uploading a file.

SiteConfig.php

namespace mymodule\siteconfig;

use SilverStripe\ORM\DataExtension;
use SilverStripe\Forms\FieldList;
use SilverStripe\AssetAdmin\Forms\UploadField;

class SiteConfig extends DataExtension {

    private static $has_one = array(
        'Logo' => 'SilverStripe\\Assets\\File'
    );

    public function updateCMSFields(FieldList $fields) {

        $fields->addFieldToTab('Root.Main', $logo = UploadField::create('Logo', 'Logo upload'));

    }

}

Server's error log does not show anything relevant to this error. Whats going on here?

UPDATE

I just tried to upload a file to the Files section in the CMS, got the exact same error.

Answer 1

private static $has_one = [
    'LogoImage' => Image::class,
];

public function updateCMSFields(FieldList $fields) {

   $fields->addFieldToTab('Root.Main', UploadField::create('LogoImage', 'Logo'));

}