If there's no cover letter for a series, Patchwork still shows you the cover letter tab first when you go to the series detail which is pretty useless - ideally it would take you to the patch list for the series in that case, with some minor visual indication that there's no cover letter (perhaps grey the tab or something like that, alternative ideas welcome).
Fix can be seen at: https://lists.yoctoproject.org/pipermail/yocto/2017-September/037782.html and implementation example at staging instance: https://lists.yoctoproject.org/pipermail/yocto/2017-September/037782.html
Change is now implemented in production instance.