Javascript 联合接口类型上不存在属性

我有一个包含团队成员数组的对象，最小的对象类型实现interface Member或interface Manager.管理器对象可以包含其他interface Member个对象.每个成员/经理都有自己的key: string.

从代码中可以看出，我正在try 实现一个函数setProfession(key, profession)，该函数根据某个成员/经理的个人key: string为其设置profession: string属性.

my setProfession函数中存在以下错误:

Property 'members' does not exist on type 'Member | Manager'.

我不理解这个错误，因为我在错误所在的线路前放了一个安全防护装置.尽管interface Manager显然包含members属性，但它仍然会抛出一个错误:

interface Member {
  key: string;
  name: string;
  profession: string;
}

interface Manager {
  key: string;
  name: string;
  profession: string;
  members: Array<Member>
}

interface Team {
  members: Array<Member | Manager>
}

const TEAM: Team = {
  members: [
    {
      key: 'RodneyMcKay1',
      name: 'Rodney McKay',
      profession: 'Scientist'
    }, {
      key: 'JohnShephard1',
      name: 'John Shephard',
      profession: 'Soldier',
      members: [
        {
          key: 'TeylaEmmagan1',
          name: 'Teyla Emmagan',
          profession: 'Soldier'
        }, {
          key: 'RononDex1',
          name: 'Ronon Dex',
          profession: 'Soldier'
        }
      ]
    }
  ]
};

const isManager = (member: Member | Manager): member is Manager => {
  return member.hasOwnProperty('members');
}

const setProfession = (key: string, profession: string): boolean => {
  for (let i = 0; i < TEAM.members.length; i++) {
    if (isManager(TEAM.members[i])) {    // SAFE GUARD 
      for (let j = 0; j < TEAM.members[i].members.length; j++) {    // ERROR
         if (TEAM.members[i].members[j].key === key) {    // ERROR
           TEAM.members[i].members[j].profession = profession;    // ERROR
           return true;
         }
      }
    } else if (TEAM.members[i].key === key) {
      TEAM.members[i].profession = profession;
      return true;
    }
  }

  return false;
}