http://host/hudson/job/whatever/ws/

(note trailing '/')

will when the project has never been built display

Run a build to have Hudson create a workspace.

with a link to

http://host/hudson/job/whatever/ws/build

which is a 404. Should be

http://host/hudson/job/whatever/build

Does not occur when URL ends in ".../ws".

<a href="build">Run a build</a> to have Hudson create a workspace.

needs to be a bit smarter.