code: public Transactions getAccountTransactions(final String accountCode, final TransactionState state, final TransactionType type, final QueryParams params) {
          if (state != null) params.put("state", state.getType());
          if (type != null) params.put("type", type.getType());
  
          return doGET(Accounts.ACCOUNTS_RESOURCE + "/" + accountCode + Transactions.TRANSACTIONS_RESOURCE,
                  Transactions.class, params);
      }
docs: Lookup an account's transactions history given query params
  <p>
  Returns the account's transaction history
  
  @param accountCode recurly account id
  @param state {@link TransactionState}
  @param type {@link TransactionType}
  @param params {@link QueryParams}
  @return the transaction history associated with this account on success, null otherwise