entity_autocomplete #default_value gives 2 errors when NULL

I’ve got my custom compound field module working (D8), but I get some errors at the top of the edit page, relating to #default_value when NULL. I’m wondering if I might’ve stumbled across an instance of an issue others have encountered, here: https://www.drupal.org/project/drupal/issues/1470236

What I have are two entity_autocomplete within the compound field, referencing a taxonomy. My issue pops up with the “#default_value” for each of these if they are empty fields (NULL).

If I have this: 
'#default_value' => Term::load($items[$delta]->description_term),

I get these two errors: 

Warning: array_flip(): Can only flip STRING and INTEGER values! in DrupalCoreEntityEntityStorageBase->loadMultiple() (line 227 of core/lib/Drupal/Core/Entity/EntityStorageBase.php).
Warning: array_flip(): Can only flip STRING and INTEGER values! in DrupalCoreEntityEntityStorageBase->getFromStaticCache() (line 139 of core/lib/Drupal/Core/Entity/EntityStorageBase.php).

I tried this: 
'#default_value' => isset($items[$delta]->description_qualifier) ? $items[$delta]->description_qualifier : NULL,

But got this: InvalidArgumentException: The #default_value property has to be an entity object or an array of entity objects. 

…not sure what else to try.

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/4/feed