code: @Override
      public void setLocations(Resource... locations) {
          final List<Resource> list = new ArrayList<>();
          for (Resource r : locations) {
              if (r.exists()) {
                  list.add(r);
              } else {
                  // In our case this event is worth a DEBUG note.
                  logger.debug(
                          "The following Resource was not present (it may be "
                                  + "optional, or it's absence may lead to issues):  ",
                          r);
              }
          }
          super.setLocations(list.toArray(new Resource[0]));
      }
docs: uPortal defines some properties files in its primaryPropertyPlaceholderConfigurer bean that
  are considered (and documented) optional. The parent class
  (PropertySourcesPlaceholderConfigurer) will operate properly without them, but puts a
  significant number of WARN messages into the log. These are noisy, and could lead a new
  adopter to think that something's wrong. This method removes absent properties files from the
  collection.