code: private OpenAPIImpl modelFromReader() {
          ClassLoader cl = getContextClassLoader();
          if (cl == null) {
              cl = OpenApiServletContextListener.class.getClassLoader();
          }
          return OpenApiProcessor.modelFromReader(config, cl);
      }
docs: Instantiate the configured {@link OASModelReader} and invoke it. If no reader is configured, then return null. If a class is configured but there is an
  error either instantiating or invokig it, a {@link RuntimeException} is thrown.