code: public ListBillingGroupsResult withBillingGroups(GroupNameAndArn... billingGroups) {
          if (this.billingGroups == null) {
              setBillingGroups(new java.util.ArrayList<GroupNameAndArn>(billingGroups.length));
          }
          for (GroupNameAndArn ele : billingGroups) {
              this.billingGroups.add(ele);
          }
          return this;
      }
docs: <p>
  The list of billing groups.
  </p>
  <p>
  <b>NOTE:</b> This method appends the values to the existing list (if any). Use
  {@link #setBillingGroups(java.util.Collection)} or {@link #withBillingGroups(java.util.Collection)} if you want
  to override the existing values.
  </p>
  
  @param billingGroups
  The list of billing groups.
  @return Returns a reference to this object so that method calls can be chained together.