check for valid federation config settings or exit

backend/src/index.ts

@@ -20,6 +20,9 @@ async function main() {
 
   // start DHT hyperswarm when DHT_TOPIC is set in .env
   if (CONFIG.FEDERATION_DHT_TOPIC) {
+    if (CONFIG.FEDERATION_COMMUNITY_URL === null) {
+      throw Error(`Config-Error: missing configuration of property FEDERATION_COMMUNITY_URL`)
+    }
     // eslint-disable-next-line no-console
     console.log(
       `starting Federation on ${CONFIG.FEDERATION_DHT_TOPIC} ${