When i select product in purchase order this error is showing

Traceback (most recent call last):
  File "/home/odoo-10/odoo/odoo-10.0/odoo/http.py", line 642, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/http.py", line 684, in dispatch
    result = self._call_function(**self.params)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/http.py", line 334, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/service/model.py", line 101, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/http.py", line 327, in checked_call
    result = self.endpoint(*a, **kw)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/http.py", line 942, in __call__
    return self.method(*args, **kw)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/http.py", line 507, in response_wrap
    response = f(*args, **kw)
  File "/home/odoo-10/odoo/odoo-10.0/addons/web/controllers/main.py", line 895, in call_kw
    return self._call_kw(model, method, args, kwargs)
  File "/home/odoo-10/odoo/odoo-10.0/addons/web/controllers/main.py", line 887, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/api.py", line 689, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/api.py", line 680, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/models.py", line 5525, in onchange
    record._onchange_eval(name, field_onchange[name], result)
  File "/home/odoo-10/odoo/odoo-10.0/odoo/models.py", line 5423, in _onchange_eval
    method_res = method(self)
  File "/home/odoo-10/odoo/odoo-10.0/addons/purchase/models/purchase.py", line 790, in onchange_product_id
    self._onchange_quantity()
  File "/home/odoo-10/odoo/odoo-10.0/addons/purchase_requisition/models/purchase_requisition.py", line 276, in _onchange_quantity
    res = super(PurchaseOrderLine, self)._onchange_quantity()
  File "/home/odoo-10/odoo/odoo-10.0/addons/purchase/models/purchase.py", line 831, in _onchange_quantity
    price_unit = self.env['account.tax']._fix_tax_included_price_company(seller.price, self.product_id.supplier_taxes_id, self.taxes_id, self.company_id) if seller else 0.0
AttributeError: 'account.tax' object has no attribute '_fix_tax_included_price_company'
Please help me to resolve this issue