Impacted versions:
11.0

I don't know if it is an issue, but I think is strange.

`product_qty` is in unit of `product` : https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L240
`reserved_availability` is in unit of `stock.move` : https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L295

`move.product_qty - move.reserved_availability` seems to have no sens, no ?

https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L915
https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L917
https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L924

thank for your answer

@jco-odoo 
@alnslang 


""" In a picking with a single unavailable move, clicking on validate without filling any
        quantities should display an UserError telling the user he cannot process a picking without
        any processed quantity.
        """
        partner = self.env['res.partner'].create({'name': 'Jean'})
        picking = self.env['stock.picking'].create({
            'location_id': self.stock_location.id,
            'location_dest_id': self.customer_location.id,
            'partner_id': partner.id,
            'picking_type_id': self.env.ref('stock.picking_type_out').id,
        })
        self.env['stock.move'].create({
            'name': 'test_immediate_validate_2',
            'location_id': self.stock_location.id,
            'location_dest_id': self.customer_location.id,
            'picking_id': picking.id,
            'product_id': self.product1.id,
            'product_uom': self.uom_unit.id,
            'product_uom_qty': 10.0,
        })
        picking.action_confirm()
        picking.action_assign()
        
        with self.assertRaises(UserError):
            picking.button_validate()
    def test_set_quantity_done_1(self):