docs: public Kafka properties(Properties properties) {
  		Preconditions.checkNotNull(properties);
  		if (this.kafkaProperties == null) {
  			this.kafkaProperties = new HashMap<>();
  		}
  		this.kafkaProperties.clear();
  		properties.forEach((k, v) -> this.kafkaProperties.put((String) k, (String) v));
  		return this;
  	}