docs: @PublicEvolving
  	public boolean contains(ConfigOption<?> configOption) {
  		synchronized (this.confData){
  			// first try the current key
  			if (this.confData.containsKey(configOption.key())) {
  				return true;
  			}
  			else if (configOption.hasFallbackKeys()) {
  				// try the fallback keys
  				for (FallbackKey fallbackKey : configOption.fallbackKeys()) {
  					if (this.confData.containsKey(fallbackKey.getKey())) {
  						loggingFallback(fallbackKey, configOption);
  						return true;
  					}
  				}
  			}
  
  			return false;
  		}
  	}