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

timesheet.py

@@ -24,7 +24,8 @@ class TimesheetLine(metaclass=PoolMeta):
     def copy(cls, records, default=None):
         if default is None:
             default = {}
-        default = default.copy()
+        else:
+            default = default.copy()
         default.setdefault('invoice_line', None)
         return super(TimesheetLine, cls).copy(records, default=default)
 

work.py

@@ -93,7 +93,8 @@ class Work(metaclass=PoolMeta):
     def copy(cls, records, default=None):
         if default is None:
             default = {}
-        default = default.copy()
+        else:
+            default = default.copy()
         default.setdefault('invoice_line', None)
         return super(Work, cls).copy(records, default=default)