throw Error('Unable to find node on an unmounted component.');
      }
      if (state === MOUNTING) {
        return null;
      }
      return fiber;
    }
     If we have two possible branches, we'll walk backwards up to the root
     to see what path the root points to. On the way we may hit one of the
     special cases and we'll deal with them.
    let a: Fiber = fiber;
    let b: Fiber = alternate;
    while (true) {
      const parentA = a.return;
      if (parentA === null) {
         We'
        break;
      }
      const parentB = parentA.alternate;
      if (parentB === null) {
         The
         hap
         is 
         ove
        const nextParent = parentA.return;
        if (nextParent !== null) {
          a = b = nextParent;
          continue;
        }
         If there's no parent, we'