O3-5199: make Bill.cashier optional

[RajPrakash681]

Summary

• Bill.cashier is now optional — bills do not belong to cashiers, payments do
• Removed forced auto-assignment of cashier on bill creation in BillResource
• Updated loadBillCashPoint to handle null cashier gracefully
• Added Liquibase migration to drop NOT NULL constraint on cashier_bill.provider_id

[codecov-commenter]

Codecov Report

❌ Patch coverage is 30.00000% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.09%. Comparing base (b52412a) to head (ad90e47).

Files with missing lines	Patch %	Lines
...module/billing/web/rest/resource/BillResource.java	0.00%	14 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #157      +/-   ##
============================================
+ Coverage     27.04%   27.09%   +0.04%     
- Complexity      497      500       +3     
============================================
  Files           190      190              
  Lines          4337     4333       -4     
  Branches        492      493       +1     
============================================
+ Hits           1173     1174       +1     
+ Misses         3062     3057       -5     
  Partials        102      102              

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[NethmiRodrigo]

A couple of things:

1. Please add some tests
2. In the ReceiptGenerator, bill.getCashier() is now nullable but no null guard was added here — this NPEs when printing a receipt for a cashier-less bill
3. In SequentialReceiptNumberGenerator bill.getCashier().getId() called without null check in CASHIER and CASHIER_AND_CASH_POINT grouping cases — NPE on bill creation when cashier is null

[NethmiRodrigo]

Changeset ID openmrs.billing-005-make-bill-cashier-optional is missing the date component; project convention is openmrs.billing-005-YYYYMMDD-description (see openmrs.billing-004-20260320-add-provider-id-to-bill-payment). Also the author should be your name.

[RajPrakash681]

@NethmiRodrigo could you please take another look at this? I’ve made the changes based on your suggestions.