@JsonPropertyDescription(DESCRIPTION_PREFIX + "values from a Java heap histogram based on the number of " +
            "instances used by each class.")
    @JsonProperty("heapHistogramInstances")
    public List<DocRef> getHeapHistogramInstancesDocRefs() {
        return heapHistogramInstancesDocRefs;
    }
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