FINERACT-2550: Fix unsupported templateType returning null response

[devi-pathak2263]

Description

Fixes an issue where unsupported templateType values in retrieveApprovalTemplate(...) returned a null/empty response instead of throwing an error.

Changes

• Added explicit validation for unsupported templateType
• Throws NotSupportedLoanTemplateTypeException for invalid values

Impact

• Prevents silent failures
• Aligns behavior with other template APIs
• Improves API consistency

Additional Notes

This change aligns with existing usage of NotSupportedLoanTemplateTypeException in other template-related methods within LoansApiResource and ensures consistent error handling across APIs..

JIRA: https://issues.apache.org/jira/browse/FINERACT-2550

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[moulendra143]

Hi,

I have looked into this issue and analyzed the current implementation in LoansApiResource.retrieveApprovalTemplate(...).

It appears that when templateType is not "approval", there is no explicit validation, which results in a null/empty response being returned instead of an error.

My proposed approach is:

• Add validation for templateType at the beginning of the method
• If the value is not "approval", throw NotSupportedLoanTemplateTypeException
• Follow the same pattern already used in other template-related methods for consistency

This should ensure proper error handling and prevent silent failures.

Please let me know if this approach looks good. I can proceed with the implementation.

Thanks!