Issue #3380054: Entity lookup returns FALSE in case of no results

src/Plugin/migrate/process/EntityLookup.php

@@ -296,7 +296,15 @@ class EntityLookup extends ProcessPluginBase implements ContainerFactoryPluginIn
       });
     }
 
-    return $multiple ? array_values($results) : reset($results);
+    if ($multiple) {
+      return array_values($results);
+    }
+
+    if (empty($results)) {
+        return NULL;
+    }
+
+    return reset($results);
   }
 
 }