code: @Nullable
    public static XMLGregorianCalendar getXMLCalendarDate (@Nullable final XMLGregorianCalendar aBase)
    {
      if (aBase == null)
        return null;
      return s_aDTFactory.newXMLGregorianCalendarDate (aBase.getYear (),
                                                       aBase.getMonth (),
                                                       aBase.getDay (),
                                                       aBase.getTimezone () == 0 ? DatatypeConstants.FIELD_UNDEFINED
                                                                                 : aBase.getTimezone ());
    }
docs: Get the passed object as {@link XMLGregorianCalendar} date (without a
  time).
  
  @param aBase
  The source object. May be <code>null</code>.
  @return <code>null</code> if the parameter is <code>null</code>.