@Entity
@Table(name = "USER_PROPERTIES")
public class UserProperties implements Serializable {

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

    @ElementCollection
    @MapKeyColumn(name = "[key]", table = "USER_PROPERTIES")
    @Column(name = "[value]", table = "USER_PROPERTIES")
    @CollectionTable(name = "USER_PROPERTIES", joinColumns = @JoinColumn(name = "ID_USER"))
    private Map<String, String> properties = new HashMap<>();

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Map<String, String> getProperties() {
        return properties;
    }

    public void setProperties(Map<String, String> properties) {
        this.properties = properties;
    }
}

UserProperties up= new UserProperties();
up.getProperties().put(UserPropertiesKeys.FIRST_NAME.toString(), response.getFirst("fName"));
up.getProperties().put(UserPropertiesKeys.LAST_NAME.toString(), response.getFirst("lName"));
up.getProperties().put(UserPropertiesKeys.COMPANY.toString(), response.getFirst("company"));
up.getProperties().put(UserPropertiesKeys.EMAIL.toString(), response.getFirst("mail"));
up.getProperties().put(UserPropertiesKeys.PHONE.toString(), response.getFirst("phone"));
em.persist(up);

(Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.QueryException
Exception Description: The list of fields to insert into the table [DatabaseTable(USER_PROPERTIES)] is empty.  You must define at least one mapping for this table.
Query: InsertObjectQuery(null)

{"properties":{"mail":"mail@mail.com","first_name":"testt","phone":"987654","company":"cmp","last_name":"test"}}