fix(alerts): Handle None when parsing event exceptions (#70173)

Fixes SENTRY-Y88

Author: snigdhas

src/sentry/rules/conditions/event_attribute.py

@@ -119,7 +119,9 @@ def _get_attribute_values(self, event: GroupEvent, attr: str) -> Sequence[object
             if path[1] not in ("type", "value"):
                 return []
 
-            return [getattr(e, path[1]) for e in event.interfaces["exception"].values]
+            return [
+                getattr(e, path[1]) for e in event.interfaces["exception"].values if e is not None
+            ]
 
         elif path[0] == "error":
             # TODO: add support for error.main_thread

tests/sentry/rules/conditions/test_event_attribute.py

@@ -768,3 +768,32 @@ def test_unreal_crash_type(self):
             data={"match": MatchType.EQUAL, "attribute": "unreal.crash_type", "value": "NoCrash"}
         )
         self.assertDoesNotPass(rule, event)
+
+    def test_does_not_error_with_none(self):
+        exception = {
+            "values": [
+                None,
+                {
+                    "type": "SyntaxError",
+                    "value": "hello world",
+                    "stacktrace": {
+                        "frames": [
+                            {
+                                "filename": "example.php",
+                                "module": "example",
+                                "context_line": 'echo "hello";',
+                                "abs_path": "path/to/example.php",
+                            }
+                        ]
+                    },
+                    "thread_id": 1,
+                },
+            ]
+        }
+
+        event = self.get_event(exception=exception)
+
+        rule = self.get_rule(
+            data={"match": MatchType.EQUAL, "attribute": "exception.type", "value": "SyntaxError"}
+        )
+        self.assertPasses(rule, event)