I am working on an extension where i want to load products grid serializer inside form. I followed magento_catalog and adding below code in my ui_component form.
<fieldset name="assign_products">
<argument name="data" xsi:type="array">
<item name="config" xsi:type="array">
<item name="label" xsi:type="string" translate="true">Products in Category</item>
<item name="collapsible" xsi:type="boolean">true</item>
<item name="sortOrder" xsi:type="number">40</item>
</item>
</argument>
<container name="assign_products_container" >
<argument name="data" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="number">160</item>
</item>
</argument>
<htmlContent name="html_content">
<argument name="block" xsi:type="object">Magento\Catalog\Block\Adminhtml\Category\AssignProducts</argument>
</htmlContent>
</container>
</fieldset>
but getting this error
Fatal error: Uncaught Error: Call to a member function getProductsReadonly() on null in C:\xampp\htdocs\m22\vendor\magento\module-catalog\Block\Adminhtml\Category\Tab\Product.php:137