template engine: no session available

[jknack]

Template engine should not fail if no session is available.

default Output encode(Context ctx, Object value) throws Exception {
        ctx.flashOrNull();
        // ERROR
        ctx.sessionOrNull();
        ctx.setDefaultResponseType(MediaType.html);
        return this.render(ctx, (ModelAndView)value);
    }

io.jooby.Usage: No session available. See https://jooby.io/#session-in-memory-session
        at jars//io.jooby.Usage.noSession(Usage.java:46)
        at jars//io.jooby.SessionStore$1.findSession(SessionStore.java:41)
        at jars//io.jooby.DefaultContext.sessionOrNull(DefaultContext.java:170)