Magento 2 Fatal error after saved Category Custom Image Attribute

Question

I've added a custom image attribute to my category with Magento 2 Module Generator from https://mage2gen.com/ (Magento version 2.2) Everything is perfect, but when I upload an image to the attribute and save category, an error occurred:

Fatal error: Method Magento\Ui\TemplateEngine\Xhtml\Result::__toString() must not throw an exception, caught Error: Cannot use string offset as an array in C:\xampp\htdocs\magento2\vendor\magento\module-ui\Component\Wrapper\UiComponent.php on line 0

This is my InstallData.php

<?php
namespace Vendor\Module\Setup;
use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;
use Magento\Eav\Setup\EavSetup;
use Magento\Eav\Setup\EavSetupFactory;
class InstallData implements InstallDataInterface
{
 private $eavSetupFactory;
 public function __construct(EavSetupFactory $eavSetupFactory)
 {
 $this->eavSetupFactory = $eavSetupFactory;
 }
 public function install(
 ModuleDataSetupInterface $setup,
 ModuleContextInterface $context
 ) {
 $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);
 $eavSetup->addAttribute(
 \Magento\Catalog\Model\Category::ENTITY,
 'thumbnail_image',
 [
 'type' => 'varchar',
 'label' => 'Thumbnail Image',
 'input' => 'image',
 'sort_order' => 5,
 'source' => '',
 'global' => 0,
 'visible' => true,
 'required' => false,
 'user_defined' => false,
 'default' => '',
 'group' => 'General Information',
 'backend' => 'Magento\Catalog\Model\Category\Attribute\Backend\Image'
 ]
 );
 }
}

And the category_form.xml

<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
<fieldset name="general">
 <field name="thumbnail_image">
 <argument name="data" xsi:type="array">
 <item name="config" xsi:type="array">
 <item name="required" xsi:type="boolean">false</item>
 <item name="validation" xsi:type="array">
 <item name="required-entry" xsi:type="boolean">false</item>
 </item>
 <item name="sortOrder" xsi:type="number">5</item>
 <item name="dataType" xsi:type="string">string</item>
 <item name="formElement" xsi:type="string">fileUploader</item>
 <item name="label" translate="true" xsi:type="string">Thumbnail Image</item>
 <item name="uploaderConfig" xsi:type="array">
 <item name="url" path="catalog/category_image/upload" xsi:type="url"/>
 </item>
 <item name="elementTmpl" xsi:type="string">ui/form/element/uploader/uploader</item>
 <item name="previewTmpl" xsi:type="string">Magento_Catalog/image-preview</item>
 <item name="source" xsi:type="string">category</item>
 </item>
 </argument>
 </field>
</fieldset>

I am sure the value is saved OK (checked in database for eav_attribute, catalog_category_entity_varchar tables) and the image is uploaded into \pub\media\catalog\category

Thanks for any help!

Answer 1

You can try this fix
https://github.com/magento/magento2/issues/5438/#issuecomment-337203020

it's helped me.