private Optional<T> getSingleValue(final String value) {
        final List<T> values = converter.apply(NullSafe.singletonList(value));
        if (values.size() == 1) {
            return Optional.of(values.getFirst());
        }
        return Optional.empty();
    }
Get an identifier for the passed docRef. term is only used for logging.
docRef may be the same as term.getDocRef() or a descendant of it, as in 'in folder'.

@return The name of the doc or its uuid depending on how the {@link TermHandler} is
configured.
stroom-db-util/src/main/java/stroom/db/util/TermHandler.java