BybitRestClientApi.GetKlinesAsync() erroneously sets ExchangeWebResult.NextPageToken to null

[vladimir-range]

NextPageToken is set to null when the number of klines returned is less than the number requested. It should be set to null when the number returned is 0, because entries for some timestamps are missing on the server.

to reproduce run the following:

using Bybit.Net;
using Bybit.Net.Clients;
using CryptoExchange.Net.SharedApis;
using System.Diagnostics;

SharedSymbol symbol = new(TradingMode.Spot, "BTC", "USDT");
BybitRestClient restClient = new(options => {options.Environment = BybitEnvironment.Testnet;});

var klineClient = restClient.V5Api.SharedClient;
var interval = SharedKlineInterval.OneMinute;
var limit = klineClient.GetKlinesOptions.MaxLimit;


DateTime endTime = new(2022, 9, 9, 17, 14, 0, DateTimeKind.Utc);
GetKlinesRequest request = new(symbol, interval, endTime: endTime, limit: limit);
var res = await klineClient.GetKlinesAsync(request);
Debug.Assert(res.NextPageToken == null);

var data = res.Data.ToArray();
Debug.Assert(data.Length == 995); // less than 1000 entries has been retrieved
Debug.Assert(data[657].OpenTime == new DateTime(2022, 9, 9, 6, 17, 0, DateTimeKind.Utc));
Debug.Assert(data[658].OpenTime == new DateTime(2022, 9, 9, 6, 11, 0, DateTimeKind.Utc)); // 5 entries are missing (12-16 minutes), so Data contains fewer entries

endTime = data[994].OpenTime.AddMinutes(-1);
request = new(symbol, interval, endTime: endTime, limit: limit);
res = await klineClient.GetKlinesAsync(request);
Debug.Assert(res.Data.Count() == 1000); // however there are more records on the server

[JKorf]

Hi, thanks for the clear reproduction scenario. It's a bit weird that there is no data there, but nevertheless I've updated the logic in the latest version to work correctly.