code: public GetReservationUtilizationRequest withGroupBy(GroupDefinition... groupBy) {
          if (this.groupBy == null) {
              setGroupBy(new java.util.ArrayList<GroupDefinition>(groupBy.length));
          }
          for (GroupDefinition ele : groupBy) {
              this.groupBy.add(ele);
          }
          return this;
      }
docs: <p>
  Groups only by <code>SUBSCRIPTION_ID</code>. Metadata is included.
  </p>
  <p>
  <b>NOTE:</b> This method appends the values to the existing list (if any). Use
  {@link #setGroupBy(java.util.Collection)} or {@link #withGroupBy(java.util.Collection)} if you want to override
  the existing values.
  </p>
  
  @param groupBy
  Groups only by <code>SUBSCRIPTION_ID</code>. Metadata is included.
  @return Returns a reference to this object so that method calls can be chained together.