Thanks for reporting. I have logged a ticket
If you want to load the resource relative then you should remove that / in the path, eg
<to uri="validator:claspath:my_message_v1.xsd" />
Thanks for raising that.
Unfortunately removing the / from the URI will not work. The DefaultLSResourceResolver calls theFileUtil.onlyPath() helper method that is looking for a Windows or Unix path separator. If no separator is found, null is returned. The calling code then calls intern() on the null value causing the NPE.