Handle when a message parser returns None

mbs-messaging-umb is such a parser that returns None if a message
does not match the schema it is validating against.

module_build_service/scheduler/consumer.py

@@ -128,6 +128,8 @@ class MBSConsumer(fedmsg.consumers.FedmsgConsumer):
             super(MBSConsumer, self).validate(message)
 
     def validate_event(self, event):
+        if event is None:
+            raise IgnoreMessage("Ignoring the message since it is null")
         # task_id is required for koji_build_change event
         if event["event"] == "koji_build_change" and event["task_id"] is None:
             raise IgnoreMessage(

tests/test_scheduler/test_consumer.py

@@ -3,7 +3,9 @@
 from __future__ import absolute_import
 
 from mock import patch, MagicMock
+import pytest
 
+from module_build_service.common.errors import IgnoreMessage
 from module_build_service.scheduler import events
 from module_build_service.scheduler.consumer import MBSConsumer
 
@@ -102,3 +104,9 @@ class TestConsumer:
         consumer.get_abstracted_event_info.return_value = event
         consumer.consume({})
         assert process_message.call_count == 0
+
+    def test_validate_event_none_msg(self):
+        hub = MagicMock(config={})
+        consumer = MBSConsumer(hub)
+        with pytest.raises(IgnoreMessage):
+            consumer.validate_event(None)