Support custom entities in product compare list

[Amadeco]

Good afternoon,

To reproduce this issue :
1- You need to have at least one custom entity defined in your administration
2- In Catalog attribute configuration, after selecting your catalog product attribute, in "Storefront Properties", you must select "Comparable on Storefront" to Yes.
3- In your frontend, add a product to the compare list with custom entity defined previously in the admin
4- Display the compare list

You must have an error :

Exception #0 (Exception): Notice: Array to string conversion in /home/amadeco/public_html/Future/vendor/magento/module-catalog/Block/Product/Compare/ListCompare.php on line 209

This error is produced by
getProductAttributeValue function
in magento/module-catalog/Block/Product/Compare/ListCompare.php

The custom entity value return an array, a string is expected.

Not sure if we need to define a plugin to correct this issue with a conditional approach.
$attribute->getFrontendInput() == 'smile_custom_entity'
or if we have a proper solution to handle this case.

Ilan Parmentier