code: public Membership set(Membership m) {
          clear();
          if(m != null)
              add(m.getMembers());
          return this;
      }
docs: Clears the membership and adds all members of a given membership parameter. Prior to setting
  membership this method will clear out all the old members of this membership by invoking the
  {@code clear} method.
  @param m a membership containing all the members this membership will contain