public boolean isSplittable(ConfigResource.Type type, String key) {
        ConfigDef configDef = configDefs.get(type);
        if (configDef == null) return false;
        ConfigDef.ConfigKey configKey = configDef.configKeys().get(key);
        if (configKey == null) return false;
        return configKey.type == ConfigDef.Type.LIST;
    }
Returns true if the configuration key specified is splittable (only lists are splittable.)
metadata/src/main/java/org/apache/kafka/metadata/KafkaConfigSchema.java