Static analysis enforces the extra isset() even though that just masks no sense.

Author: beberlei

src/UnitOfWork.php

@@ -3252,7 +3252,7 @@ private function eagerLoadCollections(array $collections, array $mapping): void
             foreach ($found as $targetValue) {
                 $sourceEntity = $targetProperty->getValue($targetValue);
 
-                if ($sourceEntity === null) {
+                if ($sourceEntity === null && isset($targetClass->associationMappings[$mappedBy]['joinColumns'])) {
                     // case where the hydration $targetValue itself has not yet fully completed, for example
                     // in case a bi-directional association is being hydrated and deferring eager loading is
                     // not possible due to subclassing.