_api/Web/Lists/getbytitle('testList')/items?$filter=(Access/Id+eq+21)

_api/Web/Lists/getbytitle('testList')/items?$filter=(Access+eq+null)

_api/Web/Lists/getbytitle('testList')/items?$filter=(Access/Id+eq+null)

<m:type>Microsoft.SharePoint.SPException</m:type>
<m:stacktrace>
at Microsoft.SharePoint.SPGlobal.HandleComException(COMException comEx) at Microsoft.SharePoint.Library.SPRequest.GetListItemDataWithCallback2(IListItemSqlClient pSqlClient, String bstrUrl, String bstrListName, String bstrViewName, String bstrViewXml, SAFEARRAYFLAGS fSafeArrayFlags, ISP2DSafeArrayWriter pSACallback, ISPDataCallback pPagingCallback, ISPDataCallback pPagingPrevCallback, ISPDataCallback pFilterLinkCallback, ISPDataCallback pSchemaCallback, ISPDataCallback pRowCountCallback, Boolean& pbMaximalView) at Microsoft.SharePoint.SPListItemCollection.EnsureListItemsData() at Microsoft.SharePoint.SPListItemEntityCollection.TryWriteAsOData(ODataWriter writer, RESTfulQuery query, ProxyContext proxyContext) at Microsoft.SharePoint.Client.ServerStub.Write(Object value, Uri path, ODataWriter writer, RESTfulQuery query, ProxyContext proxyContext) at Microsoft.SharePoint.Client.Rest.RestRequestProcessor.Process() at Microsoft.SharePoint.Client.Rest.RestRequestProcessor.ProcessRequest() at Microsoft.SharePoint.Client.Rest.RestService.ProcessQuery(Stream inputStream, IList`1 pendingDisposableContainer)
</m:stacktrace>

?$select=*,Access/Id&$expand=Access/Id&$filter=Access/Id+eq+null

?$select=*,Access/Id&$expand=Access/Id&$filter=Access/Id eq null