Malicious code vulnerability - May expose internal representation by incorporating reference to mutable object

Question

I have the following code in my dto class.

public void setBillDate(Date billDate) {
    this.billDate = billDate;
}

And I get an error in s

Answer 1

Consider using a clone as well. Don't forget null check.

public void setBillDate(Date billDate) {
    this.billDate = billDate == null ? null : billDate.clone();
}