code: @Override public synchronized Long append(final String key, final String value) throws WrongTypeException {
          checkType(key, "string");
          if (!exists(key)) {
              try {
                  set(key, value);
              }
              catch (Exception e) {
              }
          }
          else {
              stringCache.set(key, stringCache.get(key) + value);
          }
          return strlen(key);
      }
docs: /* IRedisString implementations