Avoid crashing on empty or non-existent timezone

posthog/hogql_queries/web_analytics/stats_table.py

@@ -508,7 +508,7 @@ def _counts_breakdown_value(self):
                 # Get the difference between the UNIX timestamp at UTC and the UNIX timestamp at the event's timezone
                 # Value is in milliseconds, turn it to hours, works even for fractional timezone offsets (I'm looking at you, Australia)
                 return parse_expr(
-                    "if(isNull(properties.$timezone), NULL, (toUnixTimestamp64Milli(parseDateTimeBestEffort(assumeNotNull(toString(timestamp, properties.$timezone)))) - toUnixTimestamp64Milli(timestamp)) / 3600000)"
+                    "if(or(isNull(properties.$timezone), empty(properties.$timezone)), NULL, (toUnixTimestamp64Milli(parseDateTimeBestEffort(assumeNotNull(toString(timestamp, properties.$timezone)))) - toUnixTimestamp64Milli(timestamp)) / 3600000)"
                 )
             case _:
                 raise NotImplementedError("Breakdown not implemented")

posthog/hogql_queries/web_analytics/test/test_web_stats_table.py

@@ -1099,3 +1099,49 @@ def test_timezone_filter_with_invalid_timezone(self):
                 None,
                 breakdown_by=WebStatsBreakdown.TIMEZONE,
             )
+
+    def test_timezone_filter_with_empty_timezone(self):
+        did = "id"
+        sid = str(uuid7("2019-02-17"))
+
+        _create_person(
+            team_id=self.team.pk,
+            distinct_ids=[did],
+            properties={"name": sid, "email": f"[email protected]"},
+        )
+
+        # Key not exists
+        _create_event(
+            team=self.team,
+            event="$pageview",
+            distinct_id=did,
+            timestamp=f"2019-02-17 00:00:00",
+            properties={"$session_id": sid, "$pathname": f"/path1"},
+        )
+
+        # Key exists, it's null
+        _create_event(
+            team=self.team,
+            event="$pageview",
+            distinct_id=did,
+            timestamp=f"2019-02-17 00:00:00",
+            properties={"$session_id": sid, "$pathname": f"/path1", "$timezone": None},
+        )
+
+        # Key exists, it's empty string
+        _create_event(
+            team=self.team,
+            event="$pageview",
+            distinct_id=did,
+            timestamp=f"2019-02-17 00:00:00",
+            properties={"$session_id": sid, "$pathname": f"/path1", "$timezone": ""},
+        )
+
+        results = self._run_web_stats_table_query(
+            "all",
+            None,
+            breakdown_by=WebStatsBreakdown.TIMEZONE,
+        ).results
+
+        # Don't crash, treat all of them null
+        assert results == []