hi in my odoo report for pay slip i want to count total allowance and total deduction in that 

i try with 

 <t t-set="allowance_tot" t-if="p.category_id.name == 'Indemnite' and p.total != ''" t-value="allowance_tot+p.total"/> <t t-set="deduction_tot" t-if="p.category_id.name == 'Deduction' and p.total != ''" t-value="deduction_tot+p.total"/>

and then display as 

<td><t t-esc="deduction_tot or ' '"/></td>

<td><t t-esc="allowance_tot or ' '"/></td>

it gives error like 

TypeError: unsupported operand type(s) for +: 'NoneType' and 'float'

i check value for all but not a single value in blank still it gives error