I'm getting this error while trying to open Mass Mailing module. This is not happened before.

Traceback (most recent call last):
  File "/opt/odoo/odoo-10.0/odoo/http.py", line 641, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/opt/odoo/odoo-10.0/odoo/http.py", line 683, in dispatch
    result = self._call_function(**self.params)
  File "/opt/odoo/odoo-10.0/odoo/http.py", line 333, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/opt/odoo/odoo-10.0/odoo/service/model.py", line 101, in wrapper
    return f(dbname, *args, **kwargs)
  File "/opt/odoo/odoo-10.0/odoo/http.py", line 326, in checked_call
    result = self.endpoint(*a, **kw)
  File "/opt/odoo/odoo-10.0/odoo/http.py", line 941, in __call__
    return self.method(*args, **kw)
  File "/opt/odoo/odoo-10.0/odoo/http.py", line 506, in response_wrap
    response = f(*args, **kw)
  File "/opt/odoo/odoo-10.0/addons/web/controllers/main.py", line 832, in search_read
    return self.do_search_read(model, fields, offset, limit, domain, sort)
  File "/opt/odoo/odoo-10.0/addons/web/controllers/main.py", line 854, in do_search_read
    offset=offset or 0, limit=limit or False, order=sort or False)
  File "/opt/odoo/odoo-10.0/odoo/models.py", line 4696, in search_read
    result = records.read(fields)
  File "/opt/odoo/odoo-10.0/odoo/models.py", line 3020, in read
    values[name] = field.convert_to_read(record[name], record, use_name_get)
  File "/opt/odoo/odoo-10.0/odoo/models.py", line 5211, in __getitem__
    return self._fields[key].__get__(self, type(self))
  File "/opt/odoo/odoo-10.0/odoo/fields.py", line 910, in __get__
    self.determine_value(record)
  File "/opt/odoo/odoo-10.0/odoo/fields.py", line 1022, in determine_value
    self.compute_value(recs)
  File "/opt/odoo/odoo-10.0/odoo/fields.py", line 976, in compute_value
    self._compute_value(records)
  File "/opt/odoo/odoo-10.0/odoo/fields.py", line 967, in _compute_value
    getattr(records, self.compute)()
  File "/opt/odoo/odoo-10.0/addons/mass_mailing/models/mass_mailing.py", line 342, in _compute_total
    mass_mailing.total = len(mass_mailing.sudo().get_recipients())
  File "/opt/odoo/odoo-10.0/addons/mass_mailing/models/mass_mailing.py", line 530, in get_recipients
    res_ids = self.env[self.mailing_model].search(domain).ids
  File "/opt/odoo/odoo-10.0/odoo/models.py", line 1516, in search
    res = self._search(args, offset=offset, limit=limit, order=order, count=count)
  File "/opt/odoo/odoo-10.0/odoo/models.py", line 4221, in _search
    query = self._where_calc(args)
  File "/opt/odoo/odoo-10.0/odoo/models.py", line 4020, in _where_calc
    e = expression.expression(domain, self)
  File "/opt/odoo/odoo-10.0/odoo/osv/expression.py", line 640, in __init__
    self.expression = distribute_not(normalize_domain(domain))
  File "/opt/odoo/odoo-10.0/odoo/osv/expression.py", line 204, in normalize_domain
    assert expected == 0, 'This domain is syntactically not correct: %s' % (domain)
AssertionError: This domain is syntactically not correct: [('active', '=', 1), u'|', u'|', u'&', [u'team_id', u'=', 6], [u'opt_out', u'=', False], [u'opt_out', u'=', False]]

I couldn't find any  solution for this yet. Can anyone tell me what will be the issue ??