Address review comments

Signed-off-by: Tushar Goel <tushar.goel.dav@gmail.com>

Author: TG1999

vulnerabilities/importers/xen.py

@@ -26,9 +26,22 @@ class XenImporter(Importer):
 
     def advisory_data(self):
         data = fetch_response(self.url).json()
-        if not len(data):
+        # The data looks like this
+        # [
+        #  {
+        #   "xsas": [
+        #     {
+        #       "cve": [
+        #         "CVE-2012-5510"
+        #       ],
+        #       "title": "XSA-1: Xen security advisory",
+        #       }
+        #     ]
+        #   }
+        # ]
+        if not data:
             return []
-        xsas = data[0].get("xsas") or []
+        xsas = data[0]["xsas"]
         for xsa in xsas:
             yield from self.to_advisories(xsa)