docs: @GwtIncompatible // To be supported (synchronously).
    public CacheBuilder<K, V> refreshAfterWrite(long duration, TimeUnit unit) {
      checkNotNull(unit);
      checkState(refreshNanos == UNSET_INT, "refresh was already set to %s ns", refreshNanos);
      checkArgument(duration > 0, "duration must be positive: %s %s", duration, unit);
      this.refreshNanos = unit.toNanos(duration);
      return this;
    }