Hm, unsure. This exception was actually only triggered so far because validly non-existing attributes were not properly dealt with in our code. So it was not a matter of real-world broken documents.

Instead of adding ad-hoc tests for certain bad input, I would rather prefer a generic approach to test how webodf deals with parsing broken data, by fuzzying all attributes and seeing if at least no exception is thrown. So would like to leave this line here uncovered by a special unit test for now.