Have you tried placing your MyFacesExtensionsFilter and Tomohawk filters *before* prettyfaces? It looks like MyFacesExtensionsFilter is asking PrettyFacesWrappedResponse to encode a URL when it is not in the JSF lifecycle. We should probably fix this to prevent NPEs in situations like this.
Do you play Magic?
Get TopDecked MTG, the #1 Magic App, built by players, for players. Free to use, forever.