Can't sell downloadable products after migration

Preconditions

1. Migrate 1.9.4.2 to Magento 2.3.2

Steps to reproduce

1. In Magento 2 create a new downloadable product with downloadable links, make sure it's available and in stock
2. Navigate to frontend and try to purchase the product

Expected result

1. Product is in stock

Actual result

1. Product is not in stock

Additional notes

The default value for the eav attribute links_exist has changed to null see Magento\Downloadable\Setup\Patch\Data\UpdateLinksExistDefaultAttributeValue. The migration tool does not perform this same transformation. I ran
UPDATE eav_attribute set default_value=null where attribute_code='links_exist'; to fix it.

[victor-v-rad]

Hi @fooman

Thank you for reporting this issue. Internal ticket MC-18568 to process it

[fnogatz]

Can confirm. Came here from https://magento.stackexchange.com/a/290030/33686. The suggested SQL updates fix this.