Error:
Odoo Server Error

Traceback (most recent call last):
  File "/data/build/odoo/odoo/http.py", line 627, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/data/build/odoo/odoo/http.py", line 317, in _handle_exception
    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])
  File "/data/build/odoo/odoo/tools/pycompat.py", line 14, in reraise
    raise value
  File "/data/build/odoo/odoo/http.py", line 672, in dispatch
    result = self._call_function(**self.params)
  File "/data/build/odoo/odoo/http.py", line 353, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/data/build/odoo/odoo/service/model.py", line 93, in wrapper
    return f(dbname, *args, **kwargs)
  File "/data/build/odoo/odoo/http.py", line 346, in checked_call
    result = self.endpoint(*a, **kw)
  File "/data/build/odoo/odoo/http.py", line 917, in __call__
    return self.method(*args, **kw)
  File "/data/build/odoo/odoo/http.py", line 518, in response_wrap
    response = f(*args, **kw)
  File "/data/build/odoo/addons/web/controllers/main.py", line 1108, in call_kw
    return self._call_kw(model, method, args, kwargs)
  File "/data/build/odoo/addons/web/controllers/main.py", line 1100, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/data/build/odoo/odoo/api.py", line 400, in call_kw
    result = _call_kw_multi(method, model, args, kwargs)
  File "/data/build/odoo/odoo/api.py", line 387, in _call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/data/build/odoo/addons/base_vat/models/res_partner.py", line 444, in write
    return super(ResPartner, self).write(values)
  File "/data/build/odoo/addons/snailmail/models/res_partner.py", line 20, in write
    letter_ids = self.env['snailmail.letter'].search([('state', 'not in', ['sent', 'canceled']), ('partner_id', '=', self.id)])
  File "/data/build/odoo/odoo/fields.py", line 3471, in __get__
    raise ValueError("Expected singleton: %s" % record)
ValueError: Expected singleton: res.partner(14, 26, 33, 27, 3069, 1464, 10, 35, 18, 19, 2906, 3068, 11, 20, 22, 31, 23, 2607, 1463, 3070, 15, 34, 2610, 2907, 2908, 1571, 1, 1572, 2869, 2905, 1465, 2609, 2608, 12, 21, 25, 37, 24, 36, 30, 38, 1467, 1466, 13, 29, 28, 3067, 9, 17, 32, 16, 39, 40, 8, 7, 3, 3619)