Magento 2.4.0 Custom Link Type import issue

[5d80e7b957553]

Hi,

I've added this module https://github.com/50x/Boolfly_ProductRelation
to magento 2.4.0 in order to create additional link type to grouped products.
I want to make the association work with magento import system as in new 2.4.0 you can do it by DI.
So, in the App/Code/Boolfly/ProductRelation/etc/di.xml I've added the following:

<type name="Magento\CatalogImportExport\Model\Import\Product\LinkProcessor">
        <arguments>
            <argument name="linkNameToId" xsi:type="array">
                <item name="_customtype_" xsi:type="const">Boolfly\ProductRelation\Model\Catalog\Product\Link::LINK_TYPE_CUSTOMTYPE</item>
            </argument>
        </arguments>
    </type>

Then, after creating a grouped product and a simple product in Magento backend,
I tried to import CSV with only 2 columns: sku and customtype_skus.
No error are shown during import. No association is done.
How can I solve?

P.S. Adding other columns to CSV like upsell_skus and associated_skus works for those links but still doesn't work for customtype link
Any help would be appreciated