[IMP]GOLEM Resource Account : do not show create invoicde button when there is no linked product

golem_resource_account/models/golem_resource_reservation.py

@@ -27,6 +27,7 @@ class GolemResourceReservation(models.Model):
     """ GOLEM Resource Reservation Adaptation """
     _inherit = 'golem.resource.reservation'
 
+    resource_product_id = fields.Many2one(related='resource_id.product_tmpl_id')
     invoice_id = fields.Many2one('account.invoice')
     invoicing_state = fields.Selection(related="invoice_id.state",
                                        string="Invoicing Status", default="None")

golem_resource_account/views/golem_resource_reservation_views.xml

@@ -41,8 +41,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
       <field name='inherit_id' ref="golem_resource.golem_resource_reservation_view_form"/>
       <field name="arch" type="xml">
         <button name="state_rejected"  position="after">
+          <field name="resource_product_id" invisible="1" />
           <button name="create_invoice" type="object" string="Create Invoice" class="oe_highlight"
-            attrs="{'invisible': ['|', ('state', 'not in', 'validated'), ('id', '=', False)]}" />
+            attrs="{'invisible': ['|', ('state', '!=', 'validated'), ('resource_product_id', '=', False)]}" />
         </button>
       </field>
     </record>