code: func (r *raftLog) GetUint64(k []byte) (uint64, error) {
  	var v uint64
  	vbytes, err := r.Get(k)
  	if err == nil {
  		v = binary.BigEndian.Uint64(vbytes)
  	}
  	return v, err
  }
docs: // GetUint64 implements the Stable interface