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Failed to convert value of type 'java.lang.String' to required type 'java.lang.Integer' In jpa spring

I have the following entity persisted through h2 in a JPA spring project

public class Product implements DomainObject{
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    @Version
    private Integer version;
    private String description;
    private BigDecimal price;
    private String imageUrl;
    public Product() {
// getters and setters
I have an HTML page with a form to enter new data like this
<form class="form-horizontal" th:object="${product}"
          th:action="@{/product}" method="post">
        <input type="hidden" th:field="*{id}"/>
        <div class="form-group">
            <label class="col-sm-2 control-label">Description:</label>
            <div class="col-sm-10">
                <input type="text" class="form-control" th:field="*{description}"/>
        <div class="form-group">
            <label class="col-sm-2 control-label">Price:</label>
            <div class="col-sm-10">
                <input type="text" class="form-control" th:field="*{price}"/>
        <div class="form-group">
            <label class="col-sm-2 control-label">Image Url:</label>
            <div class="col-sm-10">
                <input type="text" class="form-control" th:field="*{imageUrl}"/>
        <div class="row">
            <button type="submit" class="btn btn-default">Submit</button>
    </form>
This is the method that's handling the post from the controller 
@PostMapping("/product")
public String saveOrUpdateProduct(Product product){
    productService.saveOrUpdate(product);
    return "redirect:/product/"+product.getId();
And this is the saveOrUpdate method in the autowired service class that handles interaction with the database
private EntityManagerFactory emf;
@PersistenceUnit
public void setEmf(EntityManagerFactory emf) {
    this.emf = emf;
@Override
public Product saveOrUpdate(Product domainObject) {
    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();
    Product savedProduct = em.merge(domainObject);
    em.getTransaction().commit();
    return savedProduct;
When I go to the HTML page with the form and I try to submit I have 
  
Failed to convert value of type 'java.lang.String' to required type 'java.lang.Integer'; 
      nested exception is java.lang.NumberFormatException: For input string: "null"
                You said this is for new data, correct?  If so, why do you have a hidden input for the id?
– Powerlord
                Dec 29, 2017 at 20:11
                What exactly does get put for this input: <input type="hidden" th:field="*{id}"/>. I suspect that id will be null when passed from controller to your template.
– tsolakp
                Dec 29, 2017 at 20:37
                Wonder where this exception comes from? maybe posting the EXCEPTION PLUS STACK TRACE would help, otherwise you want people to guess. I'm not guessing. Good luck
– user8558216
                Dec 30, 2017 at 6:52
Probably you have to annotate the param product in your controller:
@PostMapping("/product")
public String saveOrUpdateProduct(@RequestBody Product product) 
Spring Javadoc for @RequestBody
@Target(value=PARAMETER)
@Retention(value=RUNTIME)
@Documented
public @interface RequestBody
/*Annotation indicating a method parameter should be bound to the body of the
  web request. The body of the request is passed through an
  HttpMessageConverter to resolve the method argument depending on the 
  content type of the request.*/
Hope this helps!
                If i add that annotation i have this error There was an unexpected error (type=Unsupported Media Type, status=415). Content type 'application/x-www-form-urlencoded;charset=UTF-8' not supported
– MrSir
                Dec 29, 2017 at 20:16
@PostMapping("/product")
public String saveOrUpdateProduct(Product product){
    productService.saveOrUpdate(product);
    return "redirect:/product/"+product.getId();
I used to call product.getId() from the original un-merged product and it didn't have an Id yet, i solved it returning a saved Product 
@PostMapping("/product")
public String saveOrUpdateProduct(Product product){
    Product savedProduct = productService.saveOrUpdate(product);
    return "redirect:/product/"+savedProduct.getId();
        
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