[notificationqueue] Pass token headers only if not empty (#405)

Otherwise it fails when using mtls certificates.

Author: anfelbar

java/com/engflow/notificationqueue/Client.java

@@ -84,12 +84,14 @@ public static void main(String[] args) throws Exception {
     }
     try {
       final Metadata header = new Metadata();
-      Metadata.Key<String> methodKey =
-          Metadata.Key.of("x-engflow-auth-method", Metadata.ASCII_STRING_MARSHALLER);
-      header.put(methodKey, "jwt-v0");
-      Metadata.Key<String> tokenKey =
-          Metadata.Key.of("x-engflow-auth-token", Metadata.ASCII_STRING_MARSHALLER);
-      header.put(tokenKey, clientOptions.getOption("token"));
+      if (!Strings.isNullOrEmpty(clientOptions.getOption("token"))) {
+        Metadata.Key<String> methodKey =
+            Metadata.Key.of("x-engflow-auth-method", Metadata.ASCII_STRING_MARSHALLER);
+        header.put(methodKey, "jwt-v0");
+        Metadata.Key<String> tokenKey =
+            Metadata.Key.of("x-engflow-auth-token", Metadata.ASCII_STRING_MARSHALLER);
+        header.put(tokenKey, clientOptions.getOption("token"));
+      }
       pull(channel, clientOptions.getOption("queue_name"), header, forwardChannel);
     } finally {
       if (channel != null) {