AC-3062 Fix Deprecation issue in EAV indexing

Author: karyna-t

app/code/Magento/Catalog/Model/ResourceModel/Product/Indexer/Eav/Source.php

@@ -18,7 +18,7 @@
  */
 class Source extends AbstractEav
 {
-    const TRANSIT_PREFIX = 'transit_';
+    public const TRANSIT_PREFIX = 'transit_';
 
     /**
      * Catalog resource helper
@@ -441,7 +441,7 @@ private function saveDataFromSelect(\Magento\Framework\DB\Select $select, array
         $data = [];
         $query = $select->query();
         while ($row = $query->fetch()) {
-            $values = explode(',', $row['value']);
+            $values = isset($row['value']) ? explode(',', $row['value']) : [];
             foreach ($values as $valueId) {
                 if (isset($options[$row['attribute_id']][$valueId])) {
                     $data[] = [$row['entity_id'], $row['attribute_id'], $row['store_id'], $valueId, $row['source_id']];