How to use elegant code logic to make the address accessed through the Get method avoid additional errors when the parameters are passed incorrectly?

Title, for example, a link I want to visit is http://www. Xxx.com?type=class, in the product perspective, only needs to class,group two types, the user's normal operation will not trigger other types, but when the user manually enter the URL, such as http://www. Xxx.com?type=class, in the background how to gracefully handle these non-existent type to meet the user experience and do not break the code elegance?

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Title, for example, a link I want to visit is http://www. Xxx.com?type=class, in the product perspective, only needs to class,group two types, the user's normal operation will not trigger other types, but when the user manually enter the URL, such as http://www. Xxx.com?type=class, in the background how to gracefully handle these non-existent type to meet the user experience and do not break the code elegance?

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