[FIX] crm: lead to opportunity no link partner

Have a lead with a partner on it, convert it to opportunity
in the conversion wizard, tick "don't link to customer"

Before this commit, the opportunity has been linked to the
lead's partner

After this commit, the opportunity is not linked to any partner

OPW 2077692

closes odoo/odoo#38262

X-original-commit: f1d270e441320e16bf38261f64a473a5296d6719
Signed-off-by: Lucas Perais (lpe) <lpe@odoo.com>

addons/crm/wizard/crm_lead_to_opportunity.py

@@ -95,8 +95,12 @@ class Lead2OpportunityPartner(models.TransientModel):
         leads = self.env['crm.lead'].browse(vals.get('lead_ids'))
         for lead in leads:
             self_def_user = self.with_context(default_user_id=self.user_id.id)
-            partner_id = self_def_user._create_partner(
-                lead.id, self.action, vals.get('partner_id') or lead.partner_id.id)
+
+            partner_id = False
+            if self.action != 'nothing':
+                partner_id = self_def_user._create_partner(
+                    lead.id, self.action, vals.get('partner_id') or lead.partner_id.id)
+
             res = lead.convert_opportunity(partner_id, [], False)
         user_ids = vals.get('user_ids')