View Builds causes Oops if empty

[Oliver Paukstadt]

zubuntu distribution has no builds right now.

If you select "View Builds" an oops occurs.
-> https://launchpad.net/distros/zubuntu/+builds

The reference for this error is OOPS-A450.

[Dafydd Harries (daf)]

Odd traceback:

    * Module canonical.launchpad.browser.build, line 118, in setupBuildList
      self.batch = Batch(builds, start)
    * Module canonical.lp.z3batching, line 35, in __init__
      listlength = len(list)

TypeError: len() of unsized object

[Celso Providelo (cprov)]

I wonder if it simply exposes a bug we have in batching system, since we normally return 'None' for empty results instead of an empty sized object.
I'd make batching system to be aware of it instead of casting it locally to a list or other sized object in each call site.
Any objection ?