code: func (it *PoolIterator) Next() (string, *token.PlainOutput, error) {
  	if it.current >= len(it.keys) {
  		return "", nil, io.EOF
  	}
  
  	entryID := it.keys[it.current]
  	it.current++
  	entry, err := it.pool.OutputByID(entryID)
  
  	return entryID, entry, err
  }
docs: // Next gets the next output from the pool, or io.EOF if there are no more outputs.