Fix TypeError crash in fetch_vulnerabilities when VulnerableCode is unreachable

bulk_search_by_purl() returns None when request_post() catches a network error or HTTP failure. The loop in fetch_vulnerabilities() iterated over
the result directly, crashing with TypeError: 'NoneType' is not iterable.

Add a guard that skips the batch and logs a warning when response_data
is falsy, so a VulnerableCode outage degrades gracefully instead of
aborting the entire pipeline run.

Fixes #2107

Signed-off-by: Harsh Verma <harshkardam246@gmail.com>

Author: harshverma27

scanpipe/pipes/vulnerablecode.py

@@ -223,6 +223,12 @@ def fetch_vulnerabilities(
 
     for purls_batch in chunked(get_purls(packages), chunk_size):
         response_data = bulk_search_by_purl(purls_batch)
+        if not response_data:
+            logger(
+                f"VulnerableCode did not return data for a batch of "
+                f"{len(purls_batch)} PURLs. Skipping batch."
+            )
+            continue
         for vulnerability_data in response_data:
             vulnerabilities_by_purl[vulnerability_data["purl"]] = vulnerability_data
 

scanpipe/tests/pipes/test_vulnerablecode.py

@@ -64,6 +64,23 @@ def test_scanpipe_pipes_vulnerablecode_fetch_vulnerabilities(
         django_5_0.refresh_from_db()
         self.assertEqual(1, len(django_5_0.affected_by_vulnerabilities))
 
+    @mock.patch("scanpipe.pipes.vulnerablecode.bulk_search_by_purl")
+    def test_fetch_vulnerabilities_handles_none_response(self, mock_search_by_purl):
+        """fetch_vulnerabilities must not crash when bulk_search_by_purl returns None.
+
+        This happens when VulnerableCode is unreachable or returns an error,
+        causing request_post() to return None implicitly.
+        """
+        package = make_package(self.project1, "pkg:pypi/requests@2.31.0")
+        mock_search_by_purl.return_value = None
+
+        buffer = io.StringIO()
+        fetch_vulnerabilities(packages=[package], logger=buffer.write)
+
+        package.refresh_from_db()
+        self.assertEqual([], package.affected_by_vulnerabilities)
+        self.assertIn("VulnerableCode did not return data", buffer.getvalue())
+
     def test_scanpipe_pipes_vulnerablecode_filter_vulnerabilities(self):
         data = self.data / "vulnerablecode/django-5.0_package_data.json"
         package_data = json.loads(data.read_text())