How to add more info in the results from a query on cosmos db using a dictionary?

Question

I have some data stored in Comsos db and some other in SQL. The data from SQL is retrieved every 5 minutes and is stored in a ConcurrentDictionary. I need to query the data on Cosmos and add more info to the results using the dictionary. So here is the code:

public IAsyncEnumerable<LogDto> GetLogsAsync(string tenantId, CancellationToken cancellationToken)
        {
            return _container.GetItemLinqQueryable<Log>()
                .Where(l => l.TenantId != null && l.TenantId.ToLower() == tenantId.ToLower()) 
                .Take(10)
                .Select(l => new LogDto()
                {
                    SerialId = l.SerialId,
                    SiteId = l.SiteId,
                    SiteName = _cacheService._siteDictionary[l.SiteId],
                })
                .ToFeedIterator()
                .ToAsyncEnumerable(cancellationToken);
        }

But I get the following error:

The specified query includes 'member indexer' which is currently not supported.

Is there any workaround for this? Any help is greatly appreciated.