code: func (i *FSTIterator) Current() ([]byte, uint64) {
  	curr := i.statesStack[len(i.statesStack)-1]
  	if curr.Final() {
  		var total uint64
  		for _, v := range i.valsStack {
  			total += v
  		}
  		total += curr.FinalOutput()
  		return i.keysStack, total
  	}
  	return nil, 0
  }
docs: // Current returns the key and value currently pointed to by the iterator.
  // If the iterator is not pointing at a valid value (because Iterator/Next/Seek)
  // returned an error previously, it may return nil,0.