Protect add_job (#4932)

tests/test_core.py

@@ -6,6 +6,7 @@ from unittest.mock import patch, MagicMock
 from datetime import datetime, timedelta
 
 import pytz
+import pytest
 
 import homeassistant.core as ha
 from homeassistant.exceptions import InvalidEntityFormatError
@@ -214,6 +215,11 @@ class TestHomeAssistant(unittest.TestCase):
         assert len(self.hass._pending_tasks) == 0
         assert len(call_count) == 2
 
+    def test_add_job_with_none(self):
+        """Try to add a job with None as function."""
+        with pytest.raises(ValueError):
+            self.hass.add_job(None, 'test_arg')
+
 
 class TestEvent(unittest.TestCase):
     """A Test Event class."""