code: public Credential setAccessToken(String accessToken) {
      lock.lock();
      try {
        this.accessToken = accessToken;
      } finally {
        lock.unlock();
      }
      return this;
    }
docs: Sets the access token.
  
  <p>
  Overriding is only supported for the purpose of calling the super implementation and changing
  the return type, but nothing else.
  </p>
  
  @param accessToken access token or {@code null} for none