The `sum` function needs to be given a compatible for the `start` argument. Instead of using that function for a simple sum of two elements (not `int`), lets just sum them explicitly instead. Traceback: ``` TypeError: unsupported operand type(s) for +: 'int' and 'account.analytic.plan' ``` closes odoo/odoo#151738 Signed-off-by: Raphael Collet <rco@odoo.com>