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