Improve readability as suggested in GH code review

Author: mpdude

src/Persisters/Entity/BasicEntityPersister.php

@@ -958,8 +958,17 @@ public function expandCriteriaParameters(Criteria $criteria)
                     $value = [$value];
                 }
 
-                $nonNullValues = array_diff_key($value, array_flip(array_keys($value, null, true)));
-                foreach ($nonNullValues as $item) {
+                foreach ($value as $item) {
+                    if ($item === null) {
+                        /*
+                         * Compare this to how \Doctrine\ORM\Persisters\Entity\BasicEntityPersister::getSelectConditionStatementSQL
+                         * creates the "[NOT] IN (...)" expression - for NULL values, it does _not_ insert a placeholder in the
+                         * SQL and instead adds an extra ... OR ... IS NULL condition. So we need to skip NULL values here as
+                         * well to create a parameters list that matches the SQL.
+                         */
+                        continue;
+                    }
+
                     $sqlParams = array_merge($sqlParams, PersisterHelper::convertToParameterValue($item, $this->em));
                     $sqlTypes  = array_merge($sqlTypes, PersisterHelper::inferParameterTypes($field, $item, $this->class, $this->em));
                 }