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

I wonder why none of the solutions takes null into consideration. A general, null-safe solution should look like this:

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