docs: @Nullable
      public Date getDateModified(@Nullable TimeZone timeZone)
      {
          Directory parent = getParent();
          if (parent instanceof ExifIFD0Directory) {
              TimeZone timeZoneModified = getTimeZone(TAG_OFFSET_TIME);
              return parent.getDate(TAG_DATETIME, getString(TAG_SUBSECOND_TIME),
                  (timeZoneModified != null) ? timeZoneModified : timeZone);
          } else {
              return null;
          }
      }