fix creation of consuption line

subscription.py

 from trytond.model import ModelView, fields, Workflow
-from trytond.pool import PoolMeta
+from trytond.pool import PoolMeta,Pool
 from trytond.pyson import Eval
 
 __all__ = ['Subscription']
@@ -34,9 +34,9 @@ class Subscription(metaclass=PoolMeta):
                 if (line.next_consumption_date is None
                         and not line.consumed):
                     if subscription.include:
-                        subscription.next_invoice_date = (subscription.invoice_start_date or subscription.start_date)
+                        line.next_consumption_date = (subscription.invoice_start_date or subscription.start_date)
                     else:
                         line.next_consumption_date = (line.compute_next_consumption_date())
             lines.extend(subscription.lines)
         Line.save(lines)
-        cls.save(subscriptions)
\ No newline at end of file
+        cls.save(subscriptions)