Cannot leave empty date range aggregates fields "from" or "to"

          <aggregate id="dublincore_modified_agg" type="date_range" parameter="dc:modified">
            <field schema="localisation_cv" name="dublincore_modified_agg"/>
            <properties/>
            <dateRanges>
              <dateRange key="from_now-6M_to_now" fromDate="now-6M" toDate="now"/>
              <dateRange key="from__to_now-6M" fromDate="" toDate="now-6M"/>
            </dateRanges>
          </aggregate>

 <aggregate id="dc_modified_agg" type="date_range" parameter="dc:modified">
            <field schema="default_search" name="dc_modified_agg" />
            <properties>
              <property name="format">"dd-MM-yyyy"</property>
            </properties>
            <dateRanges>
              <dateRange key="last24h" fromDate="now-24H" toDate="now"/>
              <dateRange key="lastWeek" fromDate="now-7d" toDate="now-24H"/>
              <dateRange key="lastMonth" fromDate="now-1M" toDate="now-7d"/>
              <dateRange key="lastYear" fromDate="now-1y" toDate="now-1M"/>
              <dateRange key="priorToLastYear" toDate="now-1y"/>
            </dateRanges>
          </aggregate>