The pull request fix the problem, if we have only a simple relation in "relations" table, but no entry in "element_relations" table. The value $elementRelations (line 23) has a value !="|", but $dateUpdated is null, because CacheService::getDateUpdatedFromElementRelations only shows in the element_relations table.
The problem only occurs, if you have an entry, that is not present in the default site group.
The pull request fix the problem, if we have only a simple relation in "relations" table, but no entry in "element_relations" table. The value $elementRelations (line 23) has a value !="|", but $dateUpdated is null, because CacheService::getDateUpdatedFromElementRelations only shows in the element_relations table.
The problem only occurs, if you have an entry, that is not present in the default site group.