Specifically, it serves a blank page because you haven't yet told it that the recipe controller's index method should respond to iphone-formatted requests.
具体地说，它将服务一个空白页面，因为您尚未告诉它recipe控制器的index方法应当响应iphone格式的请求。
We could add validation code to the register method to determine whether the first-name field is blank or null.
我们可以在register方法中添加验证代码，以确定名字字段是否为null。
A blank-testing method is useful, because many applications want to treat all blank inputs in the same way.
由于许多应用都希望用同样的方式来处理各种空白字符串，因此这一判定方法是有用的。
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