code: func rpcDecodeHexError(gotHex string) *btcjson.RPCError {
  	return btcjson.NewRPCError(btcjson.ErrRPCDecodeHexString,
  		fmt.Sprintf("Argument must be hexadecimal string (not %q)",
  			gotHex))
  }
docs: // rpcDecodeHexError is a convenience function for returning a nicely formatted
  // RPC error which indicates the provided hex string failed to decode.