Unable to fetch Purchase Orders when using numeric PurchaseOrderNumber

[colorninja]

SDK you're using (please complete the following information):

• Version 2.8.1
• Using custom connections

Describe the bug

Client can not fetch purchase order by PurchaseOrderNumber if it's numeric.

It must be a data type bug, but it seems like an API bug rather than the wrapper library bug, but I don't have access to Xero developer forums because you need to pay for that!

To Reproduce
Steps to reproduce the behavior:

1. Create a purchase order with a numeric PurchaseOrderNumber - eg. "19200"
2. Try to fetch if

<?php
[$po] = $this->accountingApi()->getPurchaseOrderByNumber('', '19200');

3. You get a 404 error
4. Ament the entry and add a letter to the PurchaseOrderNumber - eg. "A19200"
5. Try to fetch
6. It works now

Expected behavior
Correctly fetched purchase order by it's PurchaseOrderNumber when it's numeric