code: public Map<String, KrakenLedger> getKrakenPartialLedgerInfo(
        LedgerType ledgerType, String startTime, String endTime, Long offset, Currency... assets)
        throws IOException {
      String ledgerTypeString = (ledgerType == null) ? "all" : ledgerType.toString().toLowerCase();
      KrakenLedgerResult ledgerResult =
          kraken.ledgers(
              null,
              delimitAssets(assets),
              ledgerTypeString,
              startTime,
              endTime,
              offset,
              exchange.getExchangeSpecification().getApiKey(),
              signatureCreator,
              exchange.getNonceFactory());
      return checkResult(ledgerResult).getLedgerMap();
    }
docs: Retrieves a fraction of the ledger entries (usually a "page" of 50 entries) between the start
  date and the end date. The ledger records the activity (trades, deposit, withdrawals) of the
  account for all assets.
  
  @param assets Set of assets to restrict output to (can be null, defaults to all)
  @param ledgerType {@link LedgerType} to retrieve (can be null, defaults to all types)
  @param startTime Start Unix timestamp or ledger id of results (can be null)
  @param endTime End Unix timestamp or ledger id of results (can be null)
  @param offset Result offset (can be null)
  @return
  @throws IOException