fix calling a function that does not exists on garbage collector sigterm event

Issue: BB-752

Author: SylvainSenechal

extensions/gc/GarbageCollector.js

@@ -167,13 +167,17 @@ class GarbageCollector extends EventEmitter {
     }
 
     /**
-     * Close the lifecycle consumer
+     * Close the garbage collector consumer
      * @param {function} cb - callback function
      * @return {undefined}
      */
     close(cb) {
         this._logger.debug('closing garbage collector consumer');
-        this._consumer.close(cb);
+        if (this._consumer) {
+            this._consumer.close(cb);
+        } else {
+            cb();
+        }
     }
 
     processKafkaEntry(kafkaEntry, done) {

extensions/gc/service.js

@@ -100,7 +100,7 @@ initAndStart();
 
 process.on('SIGTERM', () => {
     logger.info('received SIGTERM, exiting');
-    garbageCollector.stop(() => {
+    garbageCollector.close(() => {
         process.exit(0);
     });
 });