Hibernate Error: - WARN - SQL Error: 0, SQLState: 42P01 ERROR: Relationship "freesell_seq" does not exist

I want to create a table automatically in PostgreSQL.it gives an error ie the relationship "freesell_seq" does not exist

import java.util.Date;

public class FreeSell implements it.aessepi.utils.db.PersistentInstance {

    private Integer id;
    private Boolean isStopSell;
    private Date startDate;
    private Date endDate;
    private Gruppo carClass;
    private Sede location;


    public FreeSell() {
        setIsStopSell(false);
    }

    public FreeSell(Integer id, Boolean isStopSell, Date startDate, Date endDate, Gruppo carClass, Sede location) {
        this.id = id;
        this.isStopSell = isStopSell;
        this.startDate = startDate;
        this.endDate = endDate;
        this.carClass = carClass;
        this.location = location;
    }

    public Integer getId() {
        return this.id;
    }

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

    public void setCarClass(Gruppo carClass) {
        this.carClass = carClass;
    }

    public Gruppo getCarClass() {
        return carClass;
    }

    public void setLocation(Sede location) {
        this.location = location;
    }

    public Sede getLocation() {
        return location;
    }

    public Boolean getIsStopSell() {
        return isStopSell;
    }

    public void setIsStopSell(Boolean isStopSell) {
        this.isStopSell = isStopSell;
    }

    public Date getStartDate() {
        return startDate;
    }

    public void setStartDate(Date startDate) {
        this.startDate = startDate;
    }

    public Date getEndDate() {
        return endDate;
    }

    public void setEndDate(Date endDate) {
        this.endDate = endDate;
    }

}