If user want to apply filter for related entities, OData service should return all entities, not only those with non-empty collection of related entities.

Example:
URL: http://localhost:8080/odata4/olingo_basic/Source/Customers/?$expand=Orders_FK0($filter=place%20eq%20%27town%27)
Result: OData returns only 2 customers (both have at least one order with place "town")
Expectation: OData should return all 4 customers (two of them should have empty list of orders)