diff --git a/commons/passive/google/google_activity_transition_event.avsc b/commons/passive/google/google_activity_transition_event.avsc
index 89b5f184..dda10c76 100644
--- a/commons/passive/google/google_activity_transition_event.avsc
+++ b/commons/passive/google/google_activity_transition_event.avsc
@@ -6,12 +6,12 @@
   "fields": [
     { "name": "time", "type": "double", "doc": "The UNIX epoch time (s) for the moment when the activity takes place.." },
     { "name": "timeReceived", "type": "double", "doc": "Device receiver timestamp in UTC (s)." },
-    { "name": "activity", "type": {
+    { "name": "activity", "type": ["null",{
       "name": "ActivityType",
       "type": "enum",
       "doc": "The detected activity of the device. \nIN_VEHICLE indicates the device is in a vehicle, such as a car. \nON_BICYCLE indicates the device is on a bicycle. \n ON_FOOT indicates the device is on a user who is walking or running. \nRUNNING indicates the device is on a user who is running. This is a sub-activity of ON_FOOT. \nSTILL indicates the device is still (not moving). \nWALKING indicates the device is on a user who is walking. This is a sub-activity of ON_FOOT.",
       "symbols": ["IN_VEHICLE", "ON_BICYCLE", "ON_FOOT", "RUNNING", "STILL", "WALKING", "UNKNOWN"]
-    }, "doc": "Gets the type of the activity of the transition.", "default": "UNKNOWN" },
+    }], "doc": "Gets the type of the activity of the transition.", "default": null },
     { "name": "transition", "type": {
       "name": "TransitionType",
       "type": "enum",