Update FieldDatatypeTrait.php

return `$currentProperty` when `$nestedPath` is `null`

src/Elasticsearch/Util/FieldDatatypeTrait.php

@@ -74,7 +74,7 @@ private function getNestedFieldPath(string $resourceClass, string $property): ?s
             ) {
                 $nestedPath = $this->getNestedFieldPath($nextResourceClass, implode('.', $properties));
 
-                return null === $nestedPath ? $nestedPath : "$currentProperty.$nestedPath";
+                return null === $nestedPath ? $currentProperty : "$currentProperty.$nestedPath";
             }
 
             if (