Replace @NotNull with @NotBlank on String fields in loan DTOs

[Tanjim003]

Summary

Replace @NotNull with @notblank on String fields in LoanCreateRequestDTO
and LoanCancellationRequestDTO.

Problem

@NotNull on String fields only blocks null values — it allows empty
strings "" and whitespace " " to pass validation silently. This meant:

• LoanCreateRequestDTO.loanType: "" passed validation and reached the
  workflow service with a meaningless empty loan type
• LoanCancellationRequestDTO.cancellationReason: "" passed validation
  with no meaningful reason provided

This is the same issue fixed in PR #69 for ClientCreateRequestDTO.

Changes

• LoanCreateRequestDTO: @NotNull → @notblank on loanType field
• LoanCancellationRequestDTO: @NotNull → @notblank on cancellationReason field
• Added descriptive validation messages to both fields

Before / After

Before: POST /api/v1/workflow/loan-origination/start with empty loanType
→ Request passed validation and reached workflow service

After: POST /api/v1/workflow/loan-origination/start with empty loanType
→ 400 Bad Request
{
"title": "VALIDATION_FAILED",
"status": 400,
"fieldErrors": {
"loanType": "Loan type is required"
}
}

Same behaviour confirmed for cancellationReason in loan cancellation endpoint.

Test Results

LoanCancellationControllerTest — 15 tests, 0 failures
LoanOriginationControllerTest — 10 tests, 0 failures
All 25 tests pass with no failures.

Related

Continues validation improvements from PR #69 which fixed
ClientCreateRequestDTO and added spring-boot-starter-validation.

[saksham869]

Hi @Tanjim003 , Tested on branch 7b7a56d locally.

LoanCancellationControllerTest — 15 tests, 0 failures
LoanOriginationControllerTest — 10 tests, 0 failures

Correct annotation — @notblank handles null + empty + whitespace for string fields. Consistent with PR #69.

Note: MifosWorkflowApplicationTests.contextLoads failure is pre-existing (baseUrl == null for Fineract config) — unrelated to this PR.

Approving.

[DavidH-1]

BLOCKED CLA NOT SIGNED

[DavidMifosA]

CLA Block Removed

[vidakovic]

FYI: see #74 for the new direction/architecture of this project

[vidakovic]

I think this is not relevant anymore.

[Tanjim003]

I think this is not relevant anymore.

Thanks for the review and for closing this , understood.

Since the project has moved to the new architecture, I'll re-check whether
the loan DTO validation gap still exists in the new module layout. If it does,
I'll open a fresh PR on dev targeting the correct module.

Appreciate the guidance !