Do not use empty contextual date to calculate active of party relation

Closes #13733
(grafted from 0e47111b92d3b435ddf22e8fa3ec4b74a06f0cb0)

--HG--
branch : 7.0

modules/party_relationship/party.py

@@ -80,7 +80,7 @@ class Relation(ModelSQL):
         pool = Pool()
         Date = pool.get('ir.date')
         context = Transaction().context
-        date = context.get('date', Date.today())
+        date = context.get('date') or Date.today()
         start_date = self.start_date or dt.date.min
         end_date = self.end_date or dt.date.max
         return start_date <= date <= end_date
@@ -90,7 +90,7 @@ class Relation(ModelSQL):
         pool = Pool()
         Date = pool.get('ir.date')
         context = Transaction().context
-        date = context.get('date', Date.today())
+        date = context.get('date') or Date.today()
         table, _ = tables[None]
         _, operator, value = domain