code: private JSONObject addAttributeFromSingleValue(HistoryKey pKey, String pAttrName, Object pValue, long pTimestamp) {
          HistoryEntry entry = getEntry(pKey,pValue,pTimestamp);
          return entry != null ?
                  addToHistoryEntryAndGetCurrentHistory(new JSONObject(), entry, pAttrName, pValue, pTimestamp) :
                  null;
      }
docs: Return a fresh map