I have an endpoint whose WSDL has the following policy:
<wsp:Policy wsu:Id="MyPolicy">
  <wsp:ExactlyOne>
    <wsp:All>
    <sp:SupportingTokens>
      <wsp:Policy>
        <sp:SamlToken  sp:IncludeToken="http://docs.oasis-open.org/ws-sx/ws-securitypolicy/200702/IncludeToken/AlwaysToRecipient">
          <wsp:Policy>
            <sp:WssSamlV20Token11/>
          </wsp:Policy>
        </sp:SamlToken>
      </wsp:Policy>
    </sp:SupportingTokens>
    </wsp:All>
  </wsp:ExactlyOne>
</wsp:Policy>

I've configured the client so that the provided SAML2 assertion is self signed.
The SamlTokenInterceptor deals with the request on server side; a RequestData instance is built up in 'processToken(Element tokenElement, final SoapMessage message)', but no signature crypto is configured in it. As a consequence the validation later fails in SignatureTrustValidator#validate(..) because no crypto can be retrieved.