avoid NPE when trying to find file storage mgmt service

java/com.sap.sailing.server/src/com/sap/sailing/server/RacingEventService.java

@@ -583,5 +583,8 @@ public interface RacingEventService extends TrackedRegattaRegistry, RegattaFetch
      */
     FileStorageService getActiveFileStorageService() throws NoCorrespondingServiceRegisteredException;
     
+    /**
+     * @return {@code null} if no service can be found in the OSGi registry
+     */
     FileStorageManagementService getFileStorageManagementService();
 }

java/com.sap.sailing.server/src/com/sap/sailing/server/impl/RacingEventServiceImpl.java

@@ -3001,6 +3001,10 @@ public class RacingEventServiceImpl implements RacingEventService, ClearStateTes
     public FileStorageManagementService getFileStorageManagementService() {
         ServiceReference<FileStorageManagementService> ref = bundleContext
                 .getServiceReference(FileStorageManagementService.class);
+        if (ref == null) {
+            logger.warning("No file storage management service registered");
+            return null;
+        }
         return bundleContext.getService(ref);
     }
 }