Unable to get field values in Before delete Trigger.

Our requirement is whenever account team member is deleted , delete it from the related opporunities team as well

 

We wrote a code on Sales Account-> Sales Account Resource -> Before Delete Trigger.

We are trying to get the account id , so we can query opportunities with this account id and delete the team members of opportunity.

 

Problem we are facing is , in before delete trigger,

 

println('Sales Account Resource Beore Delete:' + ResourceId + SalesAccountPartyId);

 

ResourceId is returned but SalesAccountPartyId is returned as null.