code: public static OASFactoryResolver instance() {
          if (instance == null) {
              synchronized (OASFactoryResolver.class) {
                  if (instance != null) {
                      return instance;
                  }
  
                  ClassLoader cl = AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
                      @Override
                      public ClassLoader run() {
                          return Thread.currentThread().getContextClassLoader();
                      }
                  });
                  if (cl == null) {
                      cl = OASFactoryResolver.class.getClassLoader();
                  }
  
                  OASFactoryResolver newInstance = loadSpi(cl);
  
                  if (newInstance == null) {
                      throw new IllegalStateException("No OASFactoryResolver implementation found!");
                  }
  
                  instance = newInstance;
              }
          }
  
          return instance;
      }
docs: Creates an OASFactoryResolver object.
  Only used internally from within {@link org.eclipse.microprofile.openapi.OASFactory}
  
  @return an instance of OASFactoryResolver