商談のトリガで以下のように書きましたところ、エラーがでました。
CopyOpportunityYakuwari: execution of AfterInsert caused by: System.NullPointerException: Attempt to de-reference a null object: Trigger.CopyOpportunityYakuwari: line 7, column 1
ご教授お願いします。

trigger CopyOpportunityYakuwari on Opportunity (after Insert) {

    for(Integer i=0; i<Trigger.new.size(); i++){
       Opportunity nw  = Trigger.new[i];
       Opportunity old = Trigger.old[i];
    
            /*
             * 「取引先責任者の役割」をコピー
             */
            List<OpportunityContactRole> contactRoleList = [
                SELECT
                  ContactId,
                  Role,
                  IsPrimary
                FROM
                  OpportunityContactRole
                WHERE
                  OpportunityId = :'old.id'
                                    
            ];
            
            List<OpportunityContactRole> newContactRoleList = new List<OpportunityContactRole>();
            for (OpportunityContactRole contactRole : contactRoleList) {
                newContactRoleList.add(new OpportunityContactRole(
                  OpportunityId = 'nw.id',
                  ContactId = contactRole.contactId,
                  Role = contactRole.role,
                  IsPrimary = contactRole.isPrimary
                ));
            }
            insert newContactRoleList;
        }
}