I installed audittrail and i found this error

File "/usr/lib/python2.7/dist-packages/openerp/addons/audittrail/audittrail.py", line 535, in execute_cr

return self.log_fct(cr, uid, model, method, fct_src, *args, **kw)

File "/usr/lib/python2.7/dist-packages/openerp/addons/audittrail/audittrail.py", line 300, in log_fct

old_values = self.get_data(cr, uid_orig, pool, res_ids, model, method)

File "/usr/lib/python2.7/dist-packages/openerp/addons/audittrail/audittrail.py", line 335, in get_data

for resource in resource_pool.read(cr, SUPERUSER_ID, res_ids, resource_pool._all_columns):

File "/usr/lib/python2.7/dist-packages/openerp/osv/orm.py", line 3718, in read

result = self._read_flat(cr, user, select, fields, context, load)

File "/usr/lib/python2.7/dist-packages/openerp/osv/orm.py", line 3841, in _read_flat

res2 = self._columns[f].get(cr, self, ids, f, user, context=context, values=res)

File "/usr/lib/python2.7/dist-packages/openerp/osv/fields.py", line 1158, in get

elif result.get(id):

AttributeError: 'NoneType' object has no attribute 'get'

how do I solve it?