tailcfg: add missing omitempty annotation to PopBrowserURL
@@ -1209,7 +1209,7 @@ type MapResponse struct {
// PopBrowserURL, if non-empty, is a URL for the client to
// open to complete an action. The client should dup suppress
// identical URLs and only open it once for the same URL.
- PopBrowserURL string
+ PopBrowserURL string `json:",omitempty"`
// Networking
