TableMetricsManager#getSizeHistogramsForAllTables() is returning empty map

public static Map<String, List<HistogramDistribution>> getSizeHistogramsForAllTables() {
        Map<String, List<HistogramDistribution>> map = new HashMap<>();
        for (Map.Entry<String, TableClientMetrics> entry : tableClientMetricsMapping.entrySet()) {
            TableHistograms tableHistograms = entry.getValue().getTableHistograms();
        }
        return map;
    }