N-N relationship with additional fields (problems persisting data)

I have an N-N relationship that works as follows:

Destination.java (N) - (N) CustomerService.java

Within this relationship there is an entity that holds the Id's of relationships, which has some more values. The name of this is ServiceItem.java

Below the entity's:

Destination.java

@Entity
@Table(name="destination")
public class Destination implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id_destination")
    private Long idDestination;

    @Column(name="tenant_id", insertable=false, updatable=false)
    private Long tenantId;

    @Column(name="appear_website")
    private Boolean dtAppearWebsite;

    @Lob
    @Column(name="description")
    @NotEmpty(message="O campo \"Descrição do Destino\" não pode estar em branco.")
    private String dtDescription;

    @OneToMany(mappedBy="destination")
    private Set<ServiceItem> serviceItem;

    //Mais campos adicionais e Getters and Setters

    public Destination() {
    }
}

CustomerService.java

@Entity
@Table(name = "customer_service")
public class CustomerService implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id_customer_service")
    private Long id;

    @Column(name = "tenant_id", insertable = false, updatable = false)
    private Long tenantId;

    @Column(name = "date_service")
    @DateTimeFormat(pattern = "dd/MM/yyyy")
    @Temporal(TemporalType.DATE)
    private Date date;

    @Column(name = "average_budget")
    private BigDecimal averageBudget;

    @Column(name = "service_situation")
    private boolean situation;

    @OneToMany(cascade = CascadeType.PERSIST, mappedBy = "customerService")
    private List<ServiceItem> serviceItem;

    @OneToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "fk_history")
    private History history;

    @Column(name = "service_observatons")
    private String serviceObservations;

    public CustomerService() {

    }

    //Mais campos adicionais e Getters and Setters

}

ServiceItem.java

@Entity
@Table(name = "service_item")
@IdClass(ServiceItemId.class)
public class ServiceItem {

    @Id
    @ManyToOne
    @JoinColumn(name="destination_id")
    private Destination destination;

    @Id
    @ManyToOne
    @JoinColumn(name="customerService_id")
    private CustomerService customerService;

    @Column(name="tenant_id", insertable=false, updatable=false)
    private Long tenantId;   

    @Column(name="value_negotiated")
    private double valueNegotiated;

    @Enumerated(EnumType.STRING)
    @Column(name="sale_type")
    private SaleType saleType;

    @Column(name="departure_date")
    @DateTimeFormat(pattern="dd/MM/yyyy")
    @Temporal(TemporalType.DATE)
    private Date departureDate;

    @Column(name="arrival_date")
    @DateTimeFormat(pattern="dd/MM/yyyy")
    @Temporal(TemporalType.DATE)
    private Date arrivalDate;

    @Column(name="requested_destination")
    private Boolean requestedDestination;

    @Column(name="negociation_observations")
    private String negociationObservations;

    public ServiceItem() {

    }

    //Getters and Setters
}

To generate the id's there is the class ServiceItemId.java

public class ServiceItemId implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long destination;
    private Long customerService;

    public Long getCustomerService() {
        return customerService;
    }
    public void setCustomerService(Long customerService) {
        this.customerService = customerService;
    }
    public Long getDestination() {
        return destination;
    }
    public void setDestination(Long destination) {
        this.destination = destination;
    }

    @Override
    public int hashCode() {
        return (int) (destination + customerService);
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof ServiceItemId){
            ServiceItemId serviceItemId = (ServiceItemId) obj;
            return serviceItemId.destination == destination && serviceItemId.customerService == customerService;
        }

        return false;
    }

}

Well, the question is when will I persist the data ...

Dez 17, 2014 4:52:27 PM org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: Servlet.service() for servlet [appServlet] in context with path [/viatge] threw exception [Request processing failed; nested exception is org.springframework.transaction.TransactionSystemException: Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.5.2.v20131113-a7346c6): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'customerService_id' cannot be null
Error Code: 1048
Call: INSERT INTO service_item (arrival_date, departure_date, negociation_observations, requested_destination, sale_type, value_negotiated, customerService_id, destination_id, tenant_id) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
    bind => [2016-08-01, 2015-10-01, teste, true, SUBMITTED_BUDGET, 3658.98, null, 1, 2]
Query: InsertObjectQuery(br.com.joocebox.model.ServiceItem@6e92b1b1)] with root cause
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'customerService_id' cannot be null
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4187)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4119)

How could you proceed in such a case?

EDITION

Come on!

My entity CustomerService (which refers to a service) has many destinations (in this case Destination ), as many destinations can belong to many CustomerService.java ).

Note that there is no @ManyToMany relationship directly between entities, but there is a class called ServiceItem that couples between the two entities.

When I persist a ServiceItem, my id for Destination is loaded, (since it already exists), the CustomerService has not yet been persisted, so it will not have an ID what is causing the problem.