In description of PublisherQosDataType and SubscriberQosDataType there is a sentence:

"Note that a null or empty QosCategory indicates best-effort."

This suggests that if one want to indicate best effort is supported, they should add an entry with NULL or empty category label. At the same time there seems to be implicit assumption that if the whole variable is set to null the best effort is the only supported QoS.

• Some additional description and/or example would be nice.
• Consider introducing the "best effort" label, instead of using null/empty as a magic number.