Updating against templates error

[LTIOfficial]

Updating against Templates from within Pootle produces the following error:
(run from http://pootle.linguisticteam.org/projects/tzm_defined/admin.html)

Cannot assign None: "TranslationProject.language" does not allow null values.

[LTIOfficial]

That may have been caused by Pootle's default selecting of all items on the page, including the drop-down selector line at the bottom.