code: private static ZonedDateTime toZonedDateTimeUtc(final long epochValue, final EpochUnits units) {
          Preconditions.checkArgument(units != null, "units must be non-null");
          final Instant instant = units.toInstant(epochValue);
          return ZonedDateTime.ofInstant(instant, ZoneOffset.UTC);
      }
docs: Returns a <code>ZonedDateTime</code> from the given epoch value.
  
  @param epoch
  value in milliseconds
  @return a <code>ZonedDateTime</code> or null if the date is not valid