code: func JoinAddrSlices(a []NetAddr, b []NetAddr) []NetAddr {
  	if len(a)+len(b) == 0 {
  		return nil
  	}
  	out := make([]NetAddr, 0, len(a)+len(b))
  	out = append(out, a...)
  	out = append(out, b...)
  	return out
  }
docs: // JoinAddrSlices joins two addr slices and returns a resulting slice