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