test : add explicit None input test for scanner normalize_severity

[tmdeveloper007]

Summary of What Needs to be Done:

Add an explicit unit test for BaseScanner.normalize_severity handling None input in backend/secuscan/scanners/base.py. The existing test_non_string_input test covers numeric input (123) but does not explicitly test None. The current behavior converts None via str(None) which produces "None" — not a known severity key — so the function returns "info". This should be made explicit.

Changes that Need to be Made:

In testing/backend/unit/test_scanners_base.py, add a new test method inside the existing TestNormalizeSeverity class:

def test_none_input_returns_info(self):
    scanner = _ConcreteScanner("task_none", None)
    assert scanner.normalize_severity(None) == "info"

Or as a standalone test function:

def test_normalize_severity_none_input():
    scanner = _ConcreteScanner("task_none", None)
    assert scanner.normalize_severity(None) == "info"

The _ConcreteScanner helper class is already defined in the test file. Import BaseScanner from backend.secuscan.scanners.base.

Impact that it would Provide:

• Clarity: None is a common input in real pipelines and the expectation should be documented explicitly
• Regression safety: ensures the str(None) behavior does not accidentally change

Note: This task is being handled by tmdeveloper007 — please assign to that account when picking it up.