Spring Data JPA findOne() change to Optional how to use this?

I'm learning SpringBoot2.0 with Java8.

And I followed some blog-making tutorial example.

The tutorial source code is:

@GetMapping("/{id}/edit")
public String edit(@PathVariable Long id, Model model) {
  model.addAttribute("categoryDto", categoryService.findOne(id));
  return "category/edit";
}

But this code is throwing this error:

categoryService.findOne(id)

I'm thinking about changing the JPA findOne() method to Optional< S >

How to solve that?

More info:

This is the categoryService method:

public Category findOne(Long id) {
  return categoryRepository.findOne(id);
}