private ConfigDefinition getTargetDef(GetConfigRequest req) {
        ConfigKey<?> configKey = req.getConfigKey();
        DefContent def = req.getDefContent();
        ConfigDefinitionKey configDefinitionKey = new ConfigDefinitionKey(configKey.getName(), configKey.getNamespace());
        if (def.isEmpty()) {
            log.log(Level.FINE, () -> TenantRepository.logPre(getId()) + ("No config schema in request for " + configKey));
            return cache.getDef(configDefinitionKey);
        } else {
            log.log(Level.FINE, () -> TenantRepository.logPre(getId()) + ("Got config schema from request, length:" + def.asList().size() + " : " + configKey));
            return new ConfigDefinition(configKey.getName(), def.asStringArray());
        }
    }
Gets a config from ZK. Returns null if not found.
configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java