Angular 12 NgOnChanges Cannot Read Property of null

I have a child component that is reading the changes of a selection from a drop down list. I’m trying to set local variables on the component based on when the selection changes and it works unless I clear out the selection, then I get:

Cannot read properties of null (reading ‘carrierStatusId’)

The code:

public carrierCorporateStatusEnum = CarrierCorporateApprovalStatus;
public carrierStatusEnum = CarrierStatus;
public carrierAddendumStatusEnum = CarrierAddendumStatus;

ngOnChanges(changes: SimpleChanges) {

if (changes.carrier.currentValue != changes.carrier.previousValue )
{
  this.carrier = changes.carrier.currentValue;
  this.corporateStatus = changes.corporateStatus.currentValue;
  this.carrierStatus = changes.carrier.currentValue.carrierStatusId;
  this.carrierAddendumStatus = changes.carrier.currentValue.addendumStatus;
}

}

I know there’s a way to check for null but I can’t quite figure it out. Think I’m making this harder than it is.

>Solution :

this.carrierStatus = changes.carrier.currentValue?.carrierStatusId;  

Add the "?" before .carrierStatusId.

But take care that this.carrierStatus will be null.