message: Fix send to address RPC
diff: @@ -595,7 +595,8 @@ static UniValue sendtoaddress(const JSONRPCRequest& request)
  }
  if (request.params.size() > 7 && !request.params[7].isNull()) {
  - if (!FeeModeFromString(request.params[7].get_str(), coin_control.m_fee_mode)) {
  + std::string estimate_mode = request.params[7].get_str();
  + if (!estimate_mode.empty() && !FeeModeFromString(estimate_mode, coin_control.m_fee_mode)) {
  throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid estimate_mode parameter");
  }
  }
  