Error:
Odoo Server Error

Traceback (most recent call last):
  File "/home/odoo/src/odoo/odoo/http.py", line 651, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/home/odoo/src/odoo/odoo/http.py", line 310, in _handle_exception
    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])
  File "/home/odoo/src/odoo/odoo/tools/pycompat.py", line 87, in reraise
    raise value
  File "/home/odoo/src/odoo/odoo/http.py", line 693, in dispatch
    result = self._call_function(**self.params)
  File "/home/odoo/src/odoo/odoo/http.py", line 342, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/odoo/src/odoo/odoo/service/model.py", line 97, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/odoo/src/odoo/odoo/http.py", line 335, in checked_call
    result = self.endpoint(*a, **kw)
  File "/home/odoo/src/odoo/odoo/http.py", line 937, in __call__
    return self.method(*args, **kw)
  File "/home/odoo/src/odoo/odoo/http.py", line 515, in response_wrap
    response = f(*args, **kw)
  File "/home/odoo/src/odoo/addons/web/controllers/main.py", line 938, in call_button
    action = self._call_kw(model, method, args, {})
  File "/home/odoo/src/odoo/addons/web/controllers/main.py", line 926, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/home/odoo/src/odoo/odoo/api.py", line 689, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/home/odoo/src/odoo/odoo/api.py", line 680, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/home/odoo/src/user/chou_sale/models/sale_order.py", line 213, in add_products_on_sale_order
    'tax_id': [(6,0, [tax] if tax else [])],
  File "/home/odoo/src/user/chou_sale/models/sale_order.py", line 105, in create_SOL
    tax_id = tax_id[0][2][0]
IndexError: list index out of range