code: public static Reader resource(String resourceName) {
          if (resourceName == null) {
              throw new NullPointerException("'null' passed instead of resource name");
          }
  
          final InputStream resourceStream = ClassLoader.getSystemResourceAsStream(resourceName);
          if (resourceStream == null) {
              throw new IllegalArgumentException(format("resource '%s' not found", resourceName));
          }
  
          return new BufferedReader(new InputStreamReader(resourceStream));
      }
docs: Helper method to read a classpath resource.