Empty query processed during indexation

[romainruaud]

Thanks to @southerncomputer I can confirm that there are queries processed with entity_id IN (NULL) clauses during index process.

Queries are looking like this in the query log :

## 2016-09-16 09:13:42
## 16820 ## QUERY
SQL: SELECT `t_default`.`entity_id`, `t_default`.`attribute_id`, COALESCE(t_store.value, t_default.value) AS `value` FROM `catalog_product_entity_decimal` AS `t_default`
 LEFT JOIN `catalog_product_entity_decimal` AS `t_store` ON t_default.entity_id = t_store.entity_id AND t_default.attribute_id = t_store.attribute_id AND t_store.store_id= 3 WHERE (t_default.store_id=0) AND (t_default.attribute_id IN (156)) AND (t_default.entity_id IN (NULL))
AFF: 0
TIME: 0.0017

This occurs on https://github.com/Smile-SA/elasticsuite/blob/master/src/module-elasticsuite-catalog/Model/Product/Indexer/Fulltext/Datasource/AttributeData.php#L46

The cause is there is no parent-child relation for the concerned products. Therefore, $allChildrenIds is empty and cause the useless request to be sent.