code: public CBORObject findAttribute(HeaderKeys label) {
          return findAttribute(label.AsCBOR(), PROTECTED | UNPROTECTED | DO_NOT_SEND);
      }
docs: Locate an attribute in one of the attribute buckets  The buckets are
  searched in the order protected, unprotected, unsent.
  
  @param label - HeaderKey enumeration value to search for
  @return - CBORObject with the value if found; otherwise null