diff --git a/homeassistant/components/todoist/calendar.py b/homeassistant/components/todoist/calendar.py
index 4caef136f3f..386e80bd061 100644
--- a/homeassistant/components/todoist/calendar.py
+++ b/homeassistant/components/todoist/calendar.py
@@ -9,6 +9,7 @@ import voluptuous as vol
 
 from homeassistant.components.calendar import PLATFORM_SCHEMA, CalendarEventDevice
 from homeassistant.const import CONF_ID, CONF_NAME, CONF_TOKEN
+from homeassistant.core import ServiceCall
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.template import DATE_STR_FORMAT
 from homeassistant.util import dt
@@ -161,7 +162,7 @@ def setup_platform(hass, config, add_entities, discovery_info=None):
 
     add_entities(project_devices)
 
-    def handle_new_task(call):
+    def handle_new_task(call: ServiceCall) -> None:
         """Call when a user creates a new Todoist Task from Home Assistant."""
         project_name = call.data[PROJECT_NAME]
         project_id = project_id_lookup[project_name]
@@ -188,12 +189,13 @@ def setup_platform(hass, config, add_entities, discovery_info=None):
             due_date = dt.parse_datetime(call.data[DUE_DATE])
             if due_date is None:
                 due = dt.parse_date(call.data[DUE_DATE])
+                if due is None:
+                    raise ValueError(f"Invalid due_date: {call.data[DUE_DATE]}")
                 due_date = datetime(due.year, due.month, due.day)
             # Format it in the manner Todoist expects
             due_date = dt.as_utc(due_date)
             date_format = "%Y-%m-%dT%H:%M%S"
-            due_date = datetime.strftime(due_date, date_format)
-            _due["date"] = due_date
+            _due["date"] = datetime.strftime(due_date, date_format)
 
         if _due:
             item.update(due=_due)
@@ -209,12 +211,15 @@ def setup_platform(hass, config, add_entities, discovery_info=None):
             due_date = dt.parse_datetime(call.data[REMINDER_DATE])
             if due_date is None:
                 due = dt.parse_date(call.data[REMINDER_DATE])
+                if due is None:
+                    raise ValueError(
+                        f"Invalid reminder_date: {call.data[REMINDER_DATE]}"
+                    )
                 due_date = datetime(due.year, due.month, due.day)
             # Format it in the manner Todoist expects
             due_date = dt.as_utc(due_date)
             date_format = "%Y-%m-%dT%H:%M:%S"
-            due_date = datetime.strftime(due_date, date_format)
-            _reminder_due["date"] = due_date
+            _reminder_due["date"] = datetime.strftime(due_date, date_format)
 
         if _reminder_due:
             api.reminders.add(item["id"], due=_reminder_due)