**Steps to reproduce:**
* Install `l10n_hr_edi` module.
* Generate an invoice and validate it.
* Generate a credit note from that invoice.
* Without a recipient bank account, try to send the credit note to Mojeracun.

**Observed behavior:**
* Two errors are raised before the XML is generated:
  1. `AttributeError: 'NoneType' object has no attribute 'get'` in `_invoice_constraints_eracun_new` when checking for whitespace in the bank account number.
  2. `ValueError: The following child node is not defined in the template: CreditNote/cac:BillingReference/cbc:IssueDate` during XML serialization.

**Cause:**
* issue 1 : https://github.com/odoo/odoo/commit/96cf6626d2b3e75637b908244cf2fa4da615c16b#diff-16f43166a8e5a637cb57b5695a1332845ba5440d989e25fcd59c828aa55cb036R81
* In the mentioned commit `_invoice_constraints_eracun_new`, `node.get('cac:PayeeFinancialAccount', {})` returns `None` instead of `{}` when the key exists but its value is explicitly set to `None` (which happens when no bank account is set). Chaining `.get()` on `None` raises `AttributeError`.
* issue 2 : https://github.com/odoo/odoo/commit/47ef0c2cb96be9fffdc4985255661807980839c6#diff-16f43166a8e5a637cb57b5695a1332845ba5440d989e25fcd59c828aa55cb036R146
* In the mentioned commit in `_ubl_add_billing_reference_nodes`, `cbc:IssueDate` was added as a direct child of `cac:BillingReference`. The UBL template only allows `cac:InvoiceDocumentReference` as a child of `BillingReference`, while `cbc:IssueDate` belongs inside `cac:InvoiceDocumentReference`.

**Fix:**
* Replace `.get('cac:PayeeFinancialAccount', {})` with `.get('cac:PayeeFinancialAccount')` to safely handle an explicitly `None` value before chaining further calls.
* Move `cbc:IssueDate` inside `cac:InvoiceDocumentReference` in the `BillingReference` node, matching the structure defined in `ubl_21_common.py`.

opw-6088424

Forward-Port-Of: odoo/odoo#258057