Context_get can misbehave for M2O.

In 5.0.11

I had a field in res.users call context_warehouse_id (many2one) as

----------------8<-------------------8<-----------------
class ResUsers(osv.osv):
    _inherit = 'res.users'

    _columns = {
        'context_warehouse_id': fields.many2one('stock.warehouse', 'Warehouse',
            help='Enter the default warehouse for this user, leave blank if user works on many warehouse'),
    }

    _defaults = {
        'context_warehouse_id': lambda *a: False,
    }
----------------8<-------------------8<-----------------
i try to login with the GTK client and i have this traceback
----------------8<-------------------8<-----------------
[2010-06-15 09:46:41,188] ERROR:orm:[01]:
[2010-06-15 09:46:41,188] ERROR:orm:[02]: Environment Information :
[2010-06-15 09:46:41,189] ERROR:orm:[03]: System : Linux-2.6.32-22-generic-i686-with-Ubuntu-10.04-lucid
[2010-06-15 09:46:41,189] ERROR:orm:[04]: OS Name : posix
[2010-06-15 09:46:41,189] ERROR:orm:[05]: Distributor ID: Ubuntu
[2010-06-15 09:46:41,189] ERROR:orm:[06]: Description: Ubuntu 10.04 LTS
[2010-06-15 09:46:41,189] ERROR:orm:[07]: Release: 10.04
[2010-06-15 09:46:41,190] ERROR:orm:[08]: Codename: lucid
[2010-06-15 09:46:41,190] ERROR:orm:[09]: Operating System Release : 2.6.32-22-generic
[2010-06-15 09:46:41,190] ERROR:orm:[10]: Operating System Version : #36-Ubuntu SMP Thu Jun 3 22:02:19 UTC 2010
[2010-06-15 09:46:41,190] ERROR:orm:[11]: Operating System Architecture : 32bit
[2010-06-15 09:46:41,190] ERROR:orm:[12]: Operating System Locale : fr_FR.UTF8
[2010-06-15 09:46:41,191] ERROR:orm:[13]: Python Version : 2.6.5
[2010-06-15 09:46:41,191] ERROR:orm:[14]: OpenERP-Server Version : 5.0.10
[2010-06-15 09:46:41,191] ERROR:orm:[15]: Last revision No. & ID :
[2010-06-15 09:46:41,191] ERROR:orm:[16]: Programming error: field '__getstate__' does not exist in object 'stock.warehouse' !
Exception in thread Thread-13:
Traceback (most recent call last):
  File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
    self.run()
  File "/home/neolog/instances/neolog/server/bin/netsvc.py", line 391, in run
    ts.mysend(result)
  File "/home/neolog/instances/neolog/server/bin/tiny_socket.py", line 50, in mysend
    msg = cPickle.dumps([msg,traceback])
  File "/usr/lib/python2.6/copy_reg.py", line 84, in _reduce_ex
    dict = getstate()
TypeError: 'bool' object is not callable
----------------8<-------------------8<-----------------

The problem is the many2one with getattr() return a browse_record or browse_null

I attach a patch to correct this behaviour

Regards,