On partner list sort by Country getting ERROR

[Jacara]

On partner list sort by Country getting ERROR.

Sales -> Address Book -> Customers window. Sort by Country.

Traceback (most recent call last):
  File "/home/jacara/Pydev-workspace/monoserp/osv/osv.py", line 57, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/jacara/Pydev-workspace/monoserp/osv/osv.py", line 140, in execute
    res = pool.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/jacara/Pydev-workspace/monoserp/osv/osv.py", line 130, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/jacara/Pydev-workspace/monoserp/osv/orm.py", line 1804, in search
    return self._search(cr, user, args, offset=offset, limit=limit, order=order, context=context, count=count)
  File "/home/jacara/Pydev-workspace/monoserp/osv/orm.py", line 4028, in _search
    order_by = self._generate_order_by(order, query)
  File "/home/jacara/Pydev-workspace/monoserp/osv/orm.py", line 3995, in _generate_order_by
    order_by_clause = self._generate_m2o_order_by(order_field, query)
  File "/home/jacara/Pydev-workspace/monoserp/osv/orm.py", line 3956, in _generate_m2o_order_by
    assert order_field_column._classic_write or getattr(order_field_column, 'store', False), "Many2one function/related fields must be stored to be used as ordering fields"
AssertionError: Many2one function/related fields must be stored to be used as ordering fields

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