EntityReferenceFieldItemList::referencedEntities() doesn't work for computed fields

The test-only patch from #5 looks very good, but I'm not sure about the fix. The proposed fix from #2 would require that every computed entity reference field item list to know that it needs to use a different trait than the standard one.

I think this should be better and actually fix all existing computed reference fields without the need for any changes on their part.

diff --git a/core/lib/Drupal/Core/Field/EntityReferenceFieldItemList.php b/core/lib/Drupal/Core/Field/EntityReferenceFieldItemList.php
index 0a53d98..3fa199b 100644
--- a/core/lib/Drupal/Core/Field/EntityReferenceFieldItemList.php
+++ b/core/lib/Drupal/Core/Field/EntityReferenceFieldItemList.php
@@ -24,7 +24,7 @@ public function getConstraints() {
    * {@inheritdoc}
    */
   public function referencedEntities() {
-    if (empty($this->list)) {
+    if ($this->isEmpty()) {
       return [];
     }

It would also mean that we don't need any change record update :)

Cool, looks good to me then :)

+++ b/core/lib/Drupal/Core/Field/EntityReferenceFieldItemList.php
@@ -24,7 +24,7 @@ public function getConstraints() {
+    if ($this->isEmpty()) {

This is an elegant fix, nice!

I also did a quick scan for other instances of empty($this->list) which could be similarly problematic, but the only occurrence in CommentFieldItemList doesn't look like it would be appropriate for use with the trait/computed values. +1 RTBC.

Committed and pushed 7896891da5 to 8.6.x and 7dfb2637ff to 8.5.x. Thanks!