Improve ModelStorage.copy

* Allow callable in copy default
* Support dotted notation in copy default
* Use setdefault in copy
* Copy default when needed
* Do not set default state in copy
* Use callable and dotted notation in copy default

issue5576
issue7648
review72291002

party.py

@@ -189,8 +189,9 @@ class Party(DeactivableMixin, ModelSQL, ModelView, MultiValueMixin):
     def copy(cls, parties, default=None):
         if default is None:
             default = {}
-        default = default.copy()
-        default['code'] = None
+        else:
+            default = default.copy()
+        default.setdefault('code', None)
         return super(Party, cls).copy(parties, default=default)
 
     @classmethod