private StringValue buildValue(MapDefinition mapDefinition, String value) {
        return StringValue.of(
                mapDefinition.getRefStreamDefinition().getPipelineDocRef().getUuid() + "|" +
                mapDefinition.getRefStreamDefinition().getStreamId() + "|" +
                mapDefinition.getMapName() + "|" +
                value
        );
    }
Make sure that it copes with a map not being in an early stream but is in a later one.
stroom-app/src/test/java/stroom/pipeline/refdata/TestReferenceData.java