fix: add fallback and validation for report and cron timezones (#17338)

* add fallback and validation for report and cron timezones

* add logging to exception catch

* Run black

Co-authored-by: Beto Dealmeida <roberto@dealmeida.net>

superset/tasks/cron_util.py

@@ -15,21 +15,29 @@
 # specific language governing permissions and limitations
 # under the License.
 
+import logging
 from datetime import datetime, timedelta, timezone as dt_timezone
 from typing import Iterator
 
-import pytz
 from croniter import croniter
+from pytz import timezone as pytz_timezone, UnknownTimeZoneError
 
 from superset import app
 
+logger = logging.getLogger(__name__)
+
 
 def cron_schedule_window(cron: str, timezone: str) -> Iterator[datetime]:
     window_size = app.config["ALERT_REPORTS_CRON_WINDOW_SIZE"]
     # create a time-aware datetime in utc
     time_now = datetime.now(tz=dt_timezone.utc)
-    tz = pytz.timezone(timezone)
-    utc = pytz.timezone("UTC")
+    try:
+        tz = pytz_timezone(timezone)
+    except UnknownTimeZoneError:
+        # fallback to default timezone
+        tz = pytz_timezone("UTC")
+        logger.warning("Timezone %s was invalid. Falling back to 'UTC'", timezone)
+    utc = pytz_timezone("UTC")
     # convert the current time to the user's local time for comparison
     time_now = time_now.astimezone(tz)
     start_at = time_now - timedelta(seconds=1)