code: @CheckForSigned
    public static long getMillis (@Nullable final XMLGregorianCalendar aCal)
    {
      final GregorianCalendar aGregorianCalendar = getGregorianCalendar (aCal);
      return aGregorianCalendar == null ? CGlobal.ILLEGAL_ULONG : aGregorianCalendar.getTimeInMillis ();
    }
docs: Get the passed {@link XMLGregorianCalendar} as milliseconds.
  
  @param aCal
  The source {@link XMLGregorianCalendar}. May be <code>null</code>.
  @return <code>{@link CGlobal#ILLEGAL_ULONG}</code> if the parameter is
  <code>null</code>.