Wondering why I can't access the AccountId through upward traversal in the below instance. This is in a Before trigger on OpportunityLineItem.

```
Set<Id> accountIds = new Set<id>();
for (OpportunityLineItem oli : Trigger.new) {
        accountIds.add(oli.opportunity.AccountId);

```

Have also tried *oli.opportunity.Account.Id* to no avail. When I debug it I get null.