public EffectiveMetaSet build() {
            if (this.effectiveTimeToMetaMap == null) {
                return EMPTY;
            } else {
                // Build the TreeSet from our de-duped data.
                // Ad we have de-duped we only need to compare on time, not metaId as well.
                this.effectiveMetas = createTreeSet();
                this.effectiveMetas.addAll(effectiveTimeToMetaMap.values());

                return new EffectiveMetaSet(this);
            }
        }
Add an {@link EffectiveMeta} to this set using its metaID and effectiveTimeMs.
It will de-dup items that have the same
{@link EffectiveMeta#getEffectiveMs()}, with the winner being the one with the highest
{@link EffectiveMeta#getId()}.
stroom-meta/stroom-meta-api/src/main/java/stroom/meta/api/EffectiveMetaSet.java