@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (((bitField0_ & 0x00000001) != 0)) {
      output.writeMessage(1, getSubscription());
    }
    if (((bitField0_ & 0x00000002) != 0)) {
      output.writeMessage(2, getUpdateMask());
    }
    if (validateOnly_ != false) {
      output.writeBool(3, validateOnly_);
    }
    getUnknownFields().writeTo(output);
  }
<pre>
Optional. If set to `true`, validates and previews the request, but doesn't
update the subscription.
</pre>

<code>bool validate_only = 3 [(.google.api.field_behavior) = OPTIONAL];</code>

@return The validateOnly.
java-workspaceevents/proto-google-cloud-workspaceevents-v1/src/main/java/com/google/apps/events/subscriptions/v1/UpdateSubscriptionRequest.java