code: public CBORObject findAttribute(CBORObject label, int where) {
          if (((where & PROTECTED) == PROTECTED) && objProtected.ContainsKey(label)) return objProtected.get(label);
          if (((where & UNPROTECTED) == UNPROTECTED) && objUnprotected.ContainsKey(label)) return objUnprotected.get(label);
          if (((where & DO_NOT_SEND) == DO_NOT_SEND) && objDontSend.ContainsKey(label)) return objDontSend.get(label);
          return null;
      }
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
  @param where which maps to search for the label
  @return - CBORObject with the value if found; otherwise null