Don't add null buckets to map
Don't add null buckets to map

IGV-2071

igvteam/igv,igvteam/igv,amwenger/igv,godotgildor/igv,itenente/igv,godotgildor/igv,itenente/igv,godotgildor/igv,godotgildor/igv,amwenger/igv,amwenger/igv,itenente/igv,amwenger/igv,igvteam/igv,godotgildor/igv,igvteam/igv,itenente/igv,itenente/igv,igvteam/igv,amwenger/igv