add test both params null.

Author: rmehta19

oauth2_http/javatests/com/google/auth/oauth2/ComputeEngineCredentialsTest.java

@@ -214,6 +214,18 @@ public void buildTokenUrl_nullBindingEnforcement() {
     assertEquals(TOKEN_URL + "?transport=mtls", softBoundTokenUrl);
   }
 
+  @Test
+  public void buildTokenUrl_nullTransport_nullBindingEnforcement() {
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder()
+            .setAuthTransport(null)
+            .setBindingEnforcement(null)
+            .build();
+    String softBoundTokenUrl = credentials.createTokenUrlWithScopes();
+
+    assertEquals(TOKEN_URL, softBoundTokenUrl);
+  }
+
   @Test
   public void buildTokenUrlSoftMtlsBound_mtls_transport() {
     ComputeEngineCredentials credentials =