Use parameter dcId as wrapper to prevent NPE (#8986)

Author: DaanHoogland

engine/api/src/main/java/org/apache/cloudstack/engine/subsystem/api/storage/EndPointSelector.java

@@ -47,5 +47,5 @@ public interface EndPointSelector {
 
     EndPoint select(DataStore store, String downloadUrl);
 
-    EndPoint findSsvm(long dcId);
+    EndPoint findSsvm(Long dcId);
 }

engine/storage/src/main/java/org/apache/cloudstack/storage/endpoint/DefaultEndPointSelector.java

@@ -338,7 +338,8 @@ protected EndPoint findEndpointForImageStorage(DataStore store) {
      * Finds an SSVM that can be used to execute a command.
      * For zone-wide image store, use SSVM for that zone. For region-wide store, we can arbitrarily pick one SSVM to do the task.
      * */
-    public EndPoint findSsvm(long dcId) {
+    @Override
+    public EndPoint findSsvm(Long dcId) {
         List<HostVO> ssAHosts = listUpAndConnectingSecondaryStorageVmHost(dcId);
         if (ssAHosts == null || ssAHosts.isEmpty()) {
             return null;