There may be cases where you are writing a validator or filter for a specific action on a specific page in a product where you need one of the attributes from UIValidationCriteria to perform your business logic. For example, suppose you're working on a 3rd level table on an info page, and in that table's toolbar, you don't want an action to appear if you're on an info page for a Generic Part. So you do the following (do not duplicate this code, but for the sake of an example...):

And that may work fine in your test cases where you're only testing an action on part details pages. But what if that action also appears in the toolbar of one of the tables on the home page, or on the products list page? Then the code above will throw a NullPointerException from those pages, since validationCriteria.getContextObject() will (correctly) return null.

There are a few things you can do to avoid this scenario. The first is to check and make sure that the values you're getting from UIValidationCriteria are not null. If a value is null, log a warning, and call super.[whatever method you're implementing](key, criteria, locale);.

The other thing you can do is when performing comparisons, use the .equals operation on the "expected" value. For example:

NOT

In general, just because a null value doesn't allow validation to proceed in your use case, that doesn't mean it should be a showstopper in every use case.