public Optional<ConfigProducer> getConfigProducer(String configId) {
        return Optional.ofNullable(id2producer.get(configId));
    }
Returns the ConfigProducer with the given id if such configId exists.

@param  configId The configId, e.g. "search.0/tld.0"
@return ConfigProducer with the given configId
config-model/src/main/java/com/yahoo/config/model/producer/AbstractConfigProducerRoot.java