code: @Nullable
    public static XMLGregorianCalendar getXMLCalendarDate (@Nullable final GregorianCalendar aBase)
    {
      if (aBase == null)
        return null;
      // Month in XMLGregorianCalendar is 1-based! Fix in 9.1.8
      return s_aDTFactory.newXMLGregorianCalendarDate (aBase.get (Calendar.YEAR),
                                                       aBase.get (Calendar.MONTH) + 1,
                                                       aBase.get (Calendar.DAY_OF_MONTH),
                                                       getTimezoneOffsetInMinutes (aBase));
    }
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>.