Typed query params of a resource are instanciated with the string value of corresponding value. For instance, with a query param name "color", i can have "blue", "red", etc... and corresponding instances are available within resource.
If the typed query param handles blank values, it can: Jersey framework instanciates it with such empty string.
But it does not work with collections of typed params. Blank values are not processed the same way: corresponding object is not instanciated and we got a null object instead.
In attachment, a class that reproduce and illustrate the problem.