HANA OData Service Filters

Exposing an OData service on HANA SP06 and attempting to filter records that have a null color results in a 400 Bad Request error. The filter built looks like this: $filter=COLOR+eq+null

The OData spec states that there isn't ISNULL support, but rather a null literal which can be used in comparisons such as the one I'm attempting.

Is the null literal not supported? Is there documentation on what filters the xsodata service exposes on HANA SP6?

Thanks!