Set warehouse by default on forecast

Closes #12717

modules/stock_forecast/forecast.py

@@ -123,6 +123,12 @@ class Forecast(Workflow, ModelSQL, ModelView):
     def default_state():
         return 'draft'
 
+    @classmethod
+    def default_warehouse(cls):
+        pool = Pool()
+        Location = pool.get('stock.location')
+        return Location.get_default_warehouse()
+
     @classmethod
     def default_destination(cls):
         Location = Pool().get('stock.location')