RunTimeException
is an unchecked exception. You can throw it, but you don't necessarily have to, unless you want to explicitly specify to the user of your API that this method can throw an unchecked exception. But even this doesn't seem to be necessary if you mention this fact (that the method can throw a RunTimeException) in the javadoc for this method.
So, in short, yes, you can throw it, but you don't have to, as it does not provide you any given advantage and costs you a few extra lines of code