规则调用方法返回error类型，无法获取到

func(m *Model) Update(tx *gorm.DB, updateSql string) error

规则：e = Model.Update(tx, sql)

返回结果：e 永远是nil，我方法实现直接返回 errors.New("Err")，还是返回nil

Start with the Model.Update method and the rule invocation shown in the report, then reproduce the call using the smallest available example. Trace how Go method return values, especially error values, are exposed to rules. Done means the rule can observe the returned error consistently, with regression coverage for the reported behavior.

Written by the indexing model from the issue text.