public OptionalInt nextEpoch(int epoch) {
        lock.readLock().lock();
        try {
            return toOptionalInt(epochs.higherKey(epoch));
        } finally {
            lock.readLock().unlock();
        }
    }
Get the earliest cached entry if one exists.
storage/src/main/java/org/apache/kafka/storage/internals/epoch/LeaderEpochFileCache.java