Getting null values in postman while fetching data from database using springboot although data is present in database, through userId/categoryId

I am trying to create a blog apis but Getting null values in postman while fetching data from database although data is present in database using springboot, when i am trying to get data by userId or categoryId. it's giving me null value as shown.

 { "postTitle": null, "postContent": null, "postImageName": null, 
"postAddedDate": null, "category": null, "user": null }

// Controller Class

@RestController
@RequestMapping("/api/")
public class PostController {

    @Autowired
    private PostService postService;

    // create
    @PostMapping("/user/{userId}/category/{categoryId}/posts")
    public ResponseEntity<PostDto> createPost(@RequestBody PostDto postDto, @PathVariable Integer userId,
            @PathVariable Integer categoryId) {

        PostDto createdPost = this.postService.createPost(postDto, userId, categoryId);
        return new ResponseEntity<PostDto>(createdPost, HttpStatus.CREATED);
    }

    // get post by user
    @GetMapping("/user/{userId}/posts")
    public ResponseEntity<List<PostDto>> getPostByUser(@PathVariable Integer userId) {
        List<PostDto> posts = this.postService.getPostByUser(userId);
        return new ResponseEntity<List<PostDto>>(posts, HttpStatus.OK);
    }

    // get post by category
    @GetMapping("/category/{categoryId}/posts")
    public ResponseEntity<Set<PostDto>> getPostByCategory(@PathVariable Integer categoryId) {
        Set<PostDto> posts = this.postService.getPostByCategory(categoryId);
        return new ResponseEntity<Set<PostDto>>(posts, HttpStatus.OK);
    }
}

//Post Entity Class

@Entity
@Table(name = "post")
@Getter
@Setter
@NoArgsConstructor
public class Post {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer postId;
    private String postTitle;
    @Column(length = 10000)
    private String postContent;
    private String postImageName;
    private Date postAddedDtae;

    @ManyToOne
    @JoinColumn(name = "category_id")
    private Category category;

    @ManyToOne
    private User user;

}

//Post Dto Class

@Getter
@Setter
@NoArgsConstructor
public class PostDto {

    private String postTitle;
    private String postContent;
    private String postImageName;
    private Date postAddedDate;

    private CategoryDto category;

    private UserDto user;

}

//Post Repo class

public interface PostRepo extends JpaRepository<Post, Integer> {

    List<Post> findByUser(User user);

    Set<Post> findByCategory(Category category);
}

//Post Service Class

public interface PostService {

// create
PostDto createPost(PostDto postDto, Integer userId, Integer categoryId);

// update
Post updatePost(PostDto postDto, Integer posId);

// getAll
List<PostDto> getAllPost();

// getSinglepost
Post getPostByid(Integer PostId);

// Delete
void deletePost(Integer postId);

// getPOstByCategory
Set<PostDto> getPostByCategory(Integer categoryId);

// getAllPostByUser
List<PostDto> getPostByUser(Integer userId);

// Search Post
List<PostDto> searchPosts(String keyword);

}

//Post ServiceImplmentation class

@Service
public class PostServiceImpl implements PostService {

    @Autowired
    private PostRepo postRepo;

    @Autowired
    private ModelMapper modelMapper;

    @Autowired
    private UserRepo userRepo;

    @Autowired
    private CategoryRepo categoryRepo;

    @Override
    public PostDto createPost(PostDto postDto, Integer userId, Integer categoryId) {

        User user = this.userRepo.findById(userId)
                .orElseThrow(() -> new ResourceNotFoundException("User", "User Id", userId));

        Category category = this.categoryRepo.findById(categoryId)
                .orElseThrow(() -> new ResourceNotFoundException("Category", "Category Id", categoryId));

        Post post = this.modelMapper.map(postDto, Post.class);
        post.setPostImageName("Default.png");
        post.setPostAddedDtae(new Date());
        post.setUser(user);
        post.setCategory(category);

        Post newPost = this.postRepo.save(post);
        return this.modelMapper.map(newPost, PostDto.class);
    }

    @Override
    public Post updatePost(PostDto postDto, Integer posId) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public List<PostDto> getAllPost() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Post getPostByid(Integer PostId) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void deletePost(Integer postId) {
        // TODO Auto-generated method stub

    }

    @Override
    public Set<PostDto> getPostByCategory(Integer categoryId) {
        Category cat = this.categoryRepo.findById(categoryId)
                .orElseThrow(() -> new ResourceNotFoundException("Category", "Category Id", categoryId));
        Set<Post> posts = this.postRepo.findByCategory(cat);

        Set<PostDto> postDtos = posts.stream().map((post) -> this.modelMapper.map(posts, PostDto.class))
                .collect(Collectors.toSet());
        return postDtos;
    }

    @Override
    public List<PostDto> getPostByUser(Integer userId) {
        User user = this.userRepo.findById(userId)
                .orElseThrow(() -> new ResourceNotFoundException("User", "User Id", userId));
        List<Post> posts = this.postRepo.findByUser(user);
        List<PostDto> postDtos = posts.stream().map((post) -> this.modelMapper.map(posts, PostDto.class))
                .collect(Collectors.toList());
        return postDtos;
    }

    @Override
    public List<PostDto> searchPosts(String keyword) {
        // TODO Auto-generated method stub
        return null;
    }

}

Please check and let me know where i am going wrong...