private String numberToMonth(final int i) {
        if (i >= 1 && i <= ALL_MONTHS_COUNT) {
            return Month.of(i)
                    .getDisplayName(TextStyle.FULL, Locale.ENGLISH);
        } else {
            return null;
        }
    }
Make sure that many threads can keep hitting the cache while another thread
periodically rebuilds it.
stroom-cache/stroom-cache-impl/src/test/java/stroom/cache/impl/TestStroomCacheImpl.java