code: func SignOrPanic(signer crypto.LocalSigner, msg []byte) []byte {
  	if signer == nil {
  		panic(errors.New("invalid signer. cannot be nil"))
  	}
  
  	sigma, err := signer.Sign(msg)
  	if err != nil {
  		panic(fmt.Errorf("failed generating signature: %s", err))
  	}
  	return sigma
  }
docs: // SignOrPanic signs a message and panics on error.