code: public final Promise get(String key) {
  		byte[] binaryKey = key.getBytes(StandardCharsets.UTF_8);
  		if (client != null) {
  			return new Promise(client.get(binaryKey));
  		}
  		if (clusteredClient != null) {
  			return new Promise(clusteredClient.get(binaryKey));
  		}
  		return Promise.resolve();
  	}
docs: Gets a content by a key.
  
  @param key
  cache key
  
  @return Promise with cached value (or null, the returned Promise also can
  be null)