Why .isNotNull(); assertions fails even though I have a controller class?

I am new to Spring Boot and testing. I am currently studying from baeldung's tutorial (https://spring.io/guides/gs/testing-web/) and I bumped into this error.

In fact, it passes when I use isNull() method. But I don't understand this because my controller class has mappings and all that. Why would it be null?

This is my controller class

Or maybe this is not how this test is supposed to be done? But they show it as follows in baeldung

Any help is appreciated.

Best,