Add find() method needed by other modules

--HG-- branch : 16.0

models/account_move.py

@@ -46,7 +46,7 @@
 
         for accdoc in self:
             acc_date = accdoc.date or today
-            period = self.env["account.period"].find(date=accdoc.date)
+            period = self.env["account.period"].find(date=acc_date)
 
             # When we are between the period end and cut-off date, force the
             # last day of the period.