用ModelMapper转换Pojo失败

Question

写了一个测试：

结果是：
java.lang.AssertionError:
Expected :bar 2 foo
Actual :null

增加getter和setter之后，可以解决问题：

    public static class FooInfo{
        String val;

        public void setVal(String val) {
            this.val = val;
        }
    }

    public static class BarInfo{
        String val;

        public String getVal() {
            return val;
        }
    }

    @Test
    public void testModelMapper(){
        BarInfo barInfo = new BarInfo();
        barInfo.val = "bar 2 foo";

        ModelMapper modelMapper = new ModelMapper();
        FooInfo fooInfo = modelMapper.map(barInfo, FooInfo.class);

        Assert.assertEquals(barInfo.val, fooInfo.val);

    }