@JsonPropertyDescription(DESCRIPTION_PREFIX + "various statistic values relating to the CPU load on the node.")
    @JsonProperty("cpu")
    public List<DocRef> getCpuDocRefs() {
        return cpuDocRefs;
    }
Create a list of {@link DocRef} objects that are associated with a single {@link InternalStatisticKey}
stroom-statistics/stroom-statistics-impl/src/main/java/stroom/statistics/impl/InternalStatisticsConfig.java