Fix the build
Whitespace cleanup. No functional changes
Fortify the async nature of the FilesTest tests.

We should null-ify the file/folder to be deleted so it is eligible for GC.
WICKET-5643 WebPageRenderer should bind a Session if redirect is required and the session is temporary.

Check for "" too.
Log as an ERROR and do nothing more to really prevent serving a response to another client

(cherry picked from commit 8e24bfbd46a37103ea635bda63988c50c84d606e)