public com.google.protobuf.ByteString getFilterBytes() {
      java.lang.Object ref = filter_;
      if (ref instanceof String) {
        com.google.protobuf.ByteString b =
            com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
        filter_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }
<pre>
Required. A query filter.

You can filter subscriptions by event type (`event_types`)
and target resource (`target_resource`).

You must specify at least one event type in your query. To filter for
multiple event types, use the `OR` operator.

To filter by both event type and target resource, use the `AND` operator
and specify the full resource name, such as
`//chat.googleapis.com/spaces/{space}`.

For example, the following queries are valid:

```
event_types:"google.workspace.chat.membership.v1.updated" OR
  event_types:"google.workspace.chat.message.v1.created"

event_types:"google.workspace.chat.message.v1.created" AND
  target_resource="//chat.googleapis.com/spaces/{space}"

( event_types:"google.workspace.chat.membership.v1.updated" OR
  event_types:"google.workspace.chat.message.v1.created" ) AND
  target_resource="//chat.googleapis.com/spaces/{space}"
```

The server rejects invalid queries with an `INVALID_ARGUMENT`
error.
</pre>

<code>string filter = 3 [(.google.api.field_behavior) = REQUIRED];</code>

@return The bytes for filter.
java-workspaceevents/proto-google-cloud-workspaceevents-v1/src/main/java/com/google/apps/events/subscriptions/v1/ListSubscriptionsRequest.java