Impossible to Filter Collection by `null` Attribute Value

[maxbucknell]

When loading an EAV collection, such as a product collection, it is impossible to filter a collection by specifying that the value of the attribute is null. This is because the collection generates an INNER JOIN, when it should be generating at least a LEFT JOIN.

I found this issue when researching magento/magento2/14312

Preconditions

This was found on 2.3-develop, and I haven't checked, but my suspicion is that it will fail on all versions of Magento 2.

Steps to reproduce

I have written a failing unit test for this: maxbucknell@b2e2904

Expected result

This query should find the product with the special price of null.

Actual result

Because of the INNER JOIN, $productCount is 0.

[magento-engcom-team]

Hi @maxbucknell. Thank you for your report.
The issue has been fixed in #14356 by @maxbucknell in 2.3-develop branch
Related commit(s):

• 7a3ea4ef23584d3dfdd1f414dad69858c3c46ac9
• 4589cb0ad644290e5e8d968b275bc5e2357bb349

The fix will be available with the upcoming 2.3.0 release.