Fix: mass attribute has to be handled differently.
Fix: mass attribute has to be handled differently.

copyliu/osmium,wffurr/osmium,osmium-org/osmium,osmium-org/osmium,wffurr/osmium,wffurr/osmium,copyliu/osmium,osmium-org/osmium,osmium-org/osmium,wffurr/osmium,copyliu/osmium