code: private Source getSourceFromUriResolver(StylesheetHandler handler)
              throws TransformerException {
          Source s = null;
              TransformerFactoryImpl processor = handler.getStylesheetProcessor();
              URIResolver uriresolver = processor.getURIResolver();
              if (uriresolver != null) {
                  String href = getHref();
                  String base = handler.getBaseIdentifier();
                  s = uriresolver.resolve(href,base);
              }
  
          return s;
      }
docs: Get the Source object for the included or imported stylesheet module
  obtained from the user's URIResolver, if there is no user provided
  URIResolver null is returned.