At present, we need to be able to instantiate without having `transaction_log_expense` in order to render the `#new` action.

It might be a little more clear in the controller https://github.com/bignerdranch/ShindigSheriff/blob/refactor_transactions_log_expense/app/controllers/transactions/log_expenses_controller.rb

In the `#new` action, we are getting an `:event_id` param from the url. 
In the `#create` action, we are getting an `:event_id` and `:transactions_log_expense` through a form. 

It definitely feels a little dirty, and I think it's because `Transactions.LogExpense` has more than one responsibility. At the same time, I want to avoid having a model object for every controller action. 

What do you think about a class method for the `#new` action?  Maybe something like 

```
module Transactions
  class LogExpensesController < ApplicationController

  def new
    @log_expense = LogExpense.find_event(params)
  end
...
```