code: function Group(groupId) {
      this.groupId = groupId;
      this.name = null;
      this.avatarUrl = null;
      this.myMembership = null;
      this.inviter = null;
  }
docs: Construct a new Group.
  
  @param {string} groupId The ID of this group.
  
  @prop {string} groupId The ID of this group.
  @prop {string} name The human-readable display name for this group.
  @prop {string} avatarUrl The mxc URL for this group's avatar.
  @prop {string} myMembership The logged in user's membership of this group
  @prop {Object} inviter Infomation about the user who invited the logged in user
  to the group, if myMembership is 'invite'.
  @prop {string} inviter.userId The user ID of the inviter