Sum Coloumn using footercallback doesn't work

cris82mi

Hi,
I'm tryng to use footercallback for sum the secound coloumn of my table (exposure) this value is a string but contain a double value.

The table is componed with just two fields the first: country the second; exposure, so I just need to sum the exposure in a total field to show in footer.

The table is filled dinamically like this:

The script is the following

var t = $('#aggrexp').DataTable();

        <% for (int u = 0; u < country_geo.length; u++) {%>
        <% DecimalFormat dfn = new DecimalFormat("#.##");
            Double temp = Double.parseDouble(exp_geo[u]);
            String exp = dfn.format(temp);%>

        <%if (country_geo[u] == null) {
                country_geo[u] = "";
            }%>
            t.row.add(['<%=country_geo[u]%>', '<%=exp%>']).draw();
        <% }%>

I see correctly the data, I see the field Total in footer but the sum is empty.
Please find below the link of JsBin: http://jsbin.com/cetemevuvo/edit?html,js,output
Could you please help me?
Thank you.