Why angular sends null value in date variable in spring boot api

I am sending form data from angular to spring boot to save in MySQL.

Form has few fields taking text and one field is date (input type=date )=>bootstrap

Bill Model

    export class Bill{
          billno:string
          date:Date
          vendorname:string
          amount:number
          description:string
} 

Angular Service for sending data to spring

onSubmit(){

  this.addBillForm.markAllAsTouched();
  if(this.addBillForm.invalid){
    console.log("Form is Invalid");
    return false;
  }
  this.datasaveService.addbill(this.addBillForm.value)
  .subscribe(
    res=>{
      console.log("Response : "+res);
    });
}



  addbill(bill:Bill):Observable<any>{
    return this.http.post<Bill>(this.addbillurl,bill);
  }

Bill Entity Class :

@Entity
@Table(name="bill_details") 
public class Bills {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="bill_id")
    private int bill_id;
    
    @Column(name="bill_no")
    private String billno;
    
    @Temporal(value=TemporalType.DATE)
    @Column(name="bill_date")
    private Date billdate;
    
    @Column(name="bill_amt")
    private int amount;
    
    @Column(name="bill_description")
    private String description;
    
    @Column(name="vendor_id")
    private long vendor_id;
    
    public Bills() {
    
    }

    public Bills(String billno, Date billdate, int amount, String description, long vendor_id) {
        super();
        this.billno = billno;
        this.billdate = billdate;
        this.amount = amount;
        this.description = description;
        this.vendor_id = vendor_id;
    }

    public String getBillno() {
        return billno;
    }

    public void setBillno(String billno) {
        this.billno = billno;
    }

    public Date getBilldate() {
        return billdate;
    }

    public void setBilldate(Date billdate) {
        this.billdate = billdate;
    }

    public int getAmount() {
        return amount;
    }

    public void setAmount(int amount) {
        this.amount = amount;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public long getBill_id() {
        return bill_id;
    }
    

    public void setBill_id(int bill_id) {
        this.bill_id = bill_id;
    }

    public long getVendor_id() {
        return vendor_id;
    }

    @Override
    public String toString() {
        return "Bills [bill_id=" + bill_id + ", billno=" + billno + ", billdate=" + billdate + ", amount=" + amount
                + ", description=" + description + ", vendor_id=" + vendor_id + "]";
    }
    
    
    

}

Spring Controller (Proving controller only because service and repository is correct)

   @PostMapping("/addbill")
    public Bills addBill(@RequestBody Bills thebill ) {
        System.out.println("Date : "+thebill.getBilldate());
        thebill.setBill_id(0);
        thebillservice.save(thebill);
        return thebill;
    }

On Printing bill object received in Request Body :

Bill Object : Bills [bill_id=0, billno=100, billdate=null, amount=5000, description=Buy Books, vendor_id=0]

After running I am getting following error message :

java.sql.SQLIntegrityConstraintViolationException: Column 'bill_date' cannot be null

Bill Date Column in Bill Entity is of type Date .

Same way i am saving vendor data which is working fine but only thing is there is no Date to save .

Can some one help me why i am getting null values for date attribute.