Junit报错：Argument(s) are different! Wanted：

/**
     * 处理注册的提交信息
     * @param spitter
     * @return
     */
    @RequestMapping(value = "/register", method = RequestMethod.POST)
    public String processRegister(Spitter spitter){
        spitterRepository.save(spitter);

        //跳转到个人信息页面
        return "redirect:/spitter/" + spitter.getUsername();
    }

    @Test
    public void shouldProcessRegistration() throws Exception {
        SpitterRepository mockRepository = mock(SpitterRepository.class);

        Spitter unsaved = new Spitter("xu", "jiafei", "dale", "123456");
        Spitter saved = new Spitter(10L,"xu", "jiafei", "dale", "123456");

        //当调用保存方法时，返回指定的数据
        when(mockRepository.save(unsaved)).thenReturn(saved);

        SpitterController spitterController = new SpitterController(mockRepository);

        MockMvc mockMvc = standaloneSetup(spitterController).build();

        mockMvc.perform(post("/spitter/register")
                .param("firstName","xu")
                .param("lastName","jiafei")
                .param("username","dale")
                .param("password","123456"))
                .andExpect(redirectedUrl("/spitter/dale"));

        //此处若不重写Spitter的Equals方法和hashCode方法时将会报错，说两次的参数传递不一样
        verify(mockRepository,atLeastOnce()).save(unsaved);
    }

Argument(s) are different! Wanted:
spitterRepository.save(
    Spitter{id=null, firstName='xu', lastName='jiafei', username='dale', password='123456'}
);
-> at test.SpitterControllerTest.shouldProcessRegistration(SpitterControllerTest.java:57)
Actual invocation has different arguments:
spitterRepository.save(
    Spitter{id=null, firstName='xu', lastName='jiafei', username='dale', password='123456'}
);
-> at com.spittr.controller.SpitterController.processRegister(SpitterController.java:51)