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