I'm not sure whether this should have a default value, or should be left empty. I've addressed the ``bulletIndent`` being optional in https://github.com/kogmbh/WebODF/pull/550/files#diff-9300bdc1cc3cc026d23590a713aa042cR246 by only adding it to the generated CSS if it has a value, which I think is more correct than this way (in my opinion :) )