code: @Nullable
    public static XMLGregorianCalendar getXMLCalendar (@Nullable final GregorianCalendar aCal)
    {
      if (aCal == null)
        return null;
      return s_aDTFactory.newXMLGregorianCalendar (aCal);
    }
docs: Get the passed {@link GregorianCalendar} as {@link XMLGregorianCalendar}.
  
  @param aCal
  Source calendar. May be <code>null</code>.
  @return <code>null</code> if the passed calendar is <code>null</code>.