Enclosure should always contain a length attribute

[GalacticCheese]

According to the RSS recommendations an enclosure must always contain 3 attributes. When I gave my object a length of 0 (which is recommended if the length cannot be determined) the length tag was omitted.

I see that there is an explicit check in the code to exclude the length attribute if the length is 0 (technically if !true). Why is this the case?