Error:
Odoo Server Error

Traceback (most recent call last):
  File "/opt/odoo/odoo/odoo/models.py", line 4956, in ensure_one
    _id, = self._ids
ValueError: too many values to unpack (expected 1)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/odoo/odoo/odoo/http.py", line 619, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/opt/odoo/odoo/odoo/http.py", line 309, in _handle_exception
    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])
  File "/opt/odoo/odoo/odoo/tools/pycompat.py", line 14, in reraise
    raise value
  File "/opt/odoo/odoo/odoo/http.py", line 664, in dispatch
    result = self._call_function(**self.params)
  File "/opt/odoo/odoo/odoo/http.py", line 345, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/opt/odoo/odoo/odoo/service/model.py", line 93, in wrapper
    return f(dbname, *args, **kwargs)
  File "/opt/odoo/odoo/odoo/http.py", line 338, in checked_call
    result = self.endpoint(*a, **kw)
  File "/opt/odoo/odoo/odoo/http.py", line 909, in __call__
    return self.method(*args, **kw)
  File "/opt/odoo/odoo/odoo/http.py", line 510, in response_wrap
    response = f(*args, **kw)
  File "/opt/odoo/odoo/addons/web/controllers/main.py", line 1323, in call_button
    action = self._call_kw(model, method, args, kwargs)
  File "/opt/odoo/odoo/addons/web/controllers/main.py", line 1311, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/opt/odoo/odoo/odoo/api.py", line 396, in call_kw
    model.flush()
  File "/opt/odoo/odoo/odoo/models.py", line 5343, in flush
    self.recompute()
  File "/opt/odoo/odoo/odoo/models.py", line 5744, in recompute
    process(next(iter(fields_to_compute)))
  File "/opt/odoo/odoo/odoo/models.py", line 5728, in process
    recs.mapped(field.name)
  File "/opt/odoo/odoo/odoo/models.py", line 5160, in mapped
    recs = recs._mapped_func(operator.itemgetter(name))
  File "/opt/odoo/odoo/odoo/models.py", line 5119, in _mapped_func
    vals = [func(rec) for rec in self]
  File "/opt/odoo/odoo/odoo/models.py", line 5119, in <listcomp>
    vals = [func(rec) for rec in self]
  File "/opt/odoo/odoo/odoo/models.py", line 5564, in __getitem__
    return self._fields[key].__get__(self, type(self))
  File "/opt/odoo/odoo/odoo/fields.py", line 950, in __get__
    self.compute_value(recs)
  File "/opt/odoo/odoo/odoo/fields.py", line 1060, in compute_value
    records._compute_field_value(self)
  File "/opt/odoo/odoo/odoo/models.py", line 3880, in _compute_field_value
    getattr(self, field.compute)()
  File "/opt/odoo/addons/ds-metaal/13.0/mrp_custom/models/purchase_order.py", line 29, in _compute_date_planned
    self.date_planned = self._subtract_business_days_from_date(self.delivery_date, 5)
  File "/opt/odoo/odoo/odoo/fields.py", line 943, in __get__
    record.ensure_one()
  File "/opt/odoo/odoo/odoo/models.py", line 4959, in ensure_one
    raise ValueError("Expected singleton: %s" % self)
ValueError: Expected singleton: purchase.order(40, 41)