Merge pull request #3978 from segmentio/jacobwsmith19-patch-1

Add example to only send events with userId

Author: stayseesong

src/connections/destinations/destination-filters.md

@@ -68,6 +68,7 @@ The following examples illustrate common destinations filters use cases:
 * [Remove internal and test events from production tools](#remove-internal-and-test-events-from-production-tools)
 * [Sample a percentage of events](#sample-a-percentage-of-events)
 * [Drop events](#drop-events)  
+* [Only send events with userId](#only-send-events-with-userid) 
 
 ### PII management
 
@@ -108,6 +109,26 @@ Using the [destination filters API](https://docs.segmentapis.com/tag/Destination
 
 [Watch this destination filters walkthrough](https://www.youtube.com/watch?v=47dhAF1Hoco){:target="_blank"} to learn how to use event names to filter events sent to destinations.
 
+### Only send events with userId
+
+Use the [Public API](https://docs.segmentapis.com/tag/Destination-Filters/){:target="_blank"} to only send events to your destination if they contain a `userId`. Here's an example of how you might format this request:
+
+```json
+{
+    "sourceId": "<SOURCE_ID>",
+    "destinationId": "<DESTIANTION_ID>",
+    "title": "Don't send event if userId is null",
+    "description": "Drop event if there is no userId on the request",
+    "if": "length( userId ) < 1 or typeof( userId ) != 'string'",
+    "actions": [
+      {
+        "type": "DROP"
+      }
+    ],
+    "enabled": true
+  }
+```
+
 ## Important notes
 
 #### Conflicting settings