Magento2 : Custom Image Attribute in Category Not Saving? - magento2

Question

I have create an custom image attribute in category and image uploaded successfully but it's saving Database. Can anyone guide me what is the issue in below code.
path:- /app/code/Catattribute/Catthumbnail/Setup/InstallData.php
namespace Catattribute\Catthumbnail\Setup;
use Magento\Eav\Setup\EavSetup;
use Magento\Eav\Setup\EavSetupFactory;
use Magento\Framework\Module\Setup\Migration;
use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;
use Magento\Catalog\Setup\CategorySetupFactory;
class InstallData implements InstallDataInterface
{
private $eavSetupFactory;
public function __construct(CategorySetupFactory $categorySetupFactory)
{
$this->categorySetupFactory = $categorySetupFactory;
}
public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
{
$installer = $setup;
$setup->startSetup();
$categorySetup = $this->categorySetupFactory->create(['setup' => $setup]);
$entityTypeId = $categorySetup->getEntityTypeId(\Magento\Catalog\Model\Category::ENTITY);
$attributeSetId = $categorySetup->getDefaultAttributeSetId($entityTypeId);
$categorySetup->removeAttribute(
\Magento\Catalog\Model\Category::ENTITY, 'image_thumb' );
$categorySetup->addAttribute(
\Magento\Catalog\Model\Category::ENTITY, 'image_thumb', [
'type' => 'varchar',
'label' => 'Thumbnail Image',
'input' => 'image',
'backend' => 'Magento\Catalog\Model\Category\Attribute\Backend\Image',
'required' => false,
'sort_order' => 5,
'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_STORE,
'group' => 'General Information',
]
);
$setup->endSetup();
}
}
path:- /app/code/Catattribute/Catthumbnail/view/adminhtml/ui_component/category_form.xml
<?xml version="1.0" encoding="UTF-8"?>
<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
<fieldset name="content">
<argument name="data" xsi:type="array">
<item name="config" xsi:type="array">
<item name="label" xsi:type="string" translate="true">Content</item>
<item name="collapsible" xsi:type="boolean">true</item>
<item name="sortOrder" xsi:type="number">10</item>
</item>
</argument>
<field name="image_thumb">
<argument name="data" xsi:type="array">
<item name="config" xsi:type="array">
<item name="dataType" xsi:type="string">string</item>
<item name="source" xsi:type="string">category</item>
<item name="label" xsi:type="string" translate="true">Thumbnail Image</item>
<item name="visible" xsi:type="boolean">true</item>
<item name="formElement" xsi:type="string">fileUploader</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="required" xsi:type="boolean">false</item>
<item name="sortOrder" xsi:type="number">40</item>
<item name="uploaderConfig" xsi:type="array">
<item name="url" xsi:type="url" path="catthumbnail/category_thumb/upload"/>
</item>
</item>
</argument>
</field>
</fieldset>
</form>