Java – 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{
    @Id
    @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>
        </div>
        <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>
        </div>
        <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>
        </div>
        <div class="row">
            <button type="submit" class="btn btn-default">Submit</button>
        </div>
    </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"