Timestamp field from firestore showing an invalid date if the field does not exist

These are my codes. selectedDate is a timestamp field:

<ListItemText
                          primary={
                            new Date(
                              user.items?.selectedDate?.seconds * 1000
                            ).toDateString() +
                            " at " +
                            new Date(
                              user.items?.selectedDate?.seconds * 1000
                            ).toLocaleTimeString()
                          }
                    />

It does show the data correctly. However, if the selectedDate does exist, it will show:

Invalid date at Invalid date

How can I fix this?