code: public String getMemberId(String nodePath) {
      MorePreconditions.checkNotBlank(nodePath);
      if (!nodePath.startsWith(path + "/")) {
        throw new IllegalArgumentException(
            String.format("Not a member of this group[%s]: %s", path, nodePath));
      }
  
      String memberId = StringUtils.substringAfterLast(nodePath, "/");
      if (!nodeScheme.isMember(memberId)) {
        throw new IllegalArgumentException(
            String.format("Not a group member: %s", memberId));
      }
  
      return memberId;
    }
docs: Returns the member id given a node path.