public LookupIdentifier getCurrentLookupIdentifier() {
        return currentLookupIdentifier;
    }
0-1 stream(s) per ref loader. Contains those streams from {@link ReferenceDataResult#getEffectiveStreams()}
that are known to contain the map being looked up or where the content of the stream is currently unknown.
A sub-set of effectiveStreams or equal to it.
stroom-pipeline/src/main/java/stroom/pipeline/refdata/ReferenceDataResult.java