我的图片表与用户表有两个onetoone关系：

图片实体：

@Entity
@Table(name = "pictures")
public class Picture implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    public int getId() {
        return id;
    }

    @OneToOne
    @JoinColumn(name = "customer_id", nullable = true)
    private User customer;

    public User getCustomer() {
        return customer;
    }

    public void setCustomer(User customer) {
        this.customer = customer;
    }

    @OneToOne
    @JoinColumn(name = "photographer_id", nullable = false)
    private User photographer;

    public User getPhotographer() {
        return photographer;
    }

    public void setPhotographer(User photographer) {
        this.photographer = photographer;
    }

    private String title;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    private String url;

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    private BigDecimal price;

    public BigDecimal getPrice() {
        return price;
    }

    public void setPrice(BigDecimal price) {
        this.price = price;
    }

    public Picture(String title,
                   String url,
                   BigDecimal price)
    {
        this.title = title;
        this.url = url;
        this.price = price;
    }

    public Picture() {
        // Empty constructor
    }
}

图片模板：

@Override
public void insert(Picture object) {
    sessionFactory.getCurrentSession().save(object);
}

如何更新这两个外键 customer_id 以及 photographer_id ?
在实体中，两个外键是一对一的关系 User 我得到的错误是 Column 'photographer_id' cannot be null