Error loading cache.manifest

I am using the latest touchkit 3 alpha 4 and vaadin 7.

If I enable HTML5 cache I get following error in the console output of my browser (Chrome):

Creating Application Cache with manifest https://localhost:7002/tourist/nullwidgetsets/null/cache.manifest
Application Cache Checking event
Application Cache Error event: Manifest fetch failed (404) https://localhost:7002/tourist/nullwidgetsets/null/cache.manifest

The application is working fine.

Am I missing something here or what could be the cause of outputing null?

/Kind regards

Edit: Typo

I filed a bug for this issue: