Fix listLoadBalancerRuleInstances api call

Author: vishesh92

engine/schema/src/main/java/com/cloud/vm/dao/UserVmDaoImpl.java

@@ -20,6 +20,7 @@
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Date;
 import java.util.Hashtable;
 import java.util.List;
@@ -786,6 +787,9 @@ public List<UserVmVO> findByUserDataId(long userdataId) {
 
     @Override
     public List<UserVmVO> listByIds(List<Long> ids) {
+        if (ids == null || ids.isEmpty()) {
+            return Collections.emptyList();
+        }
         SearchCriteria<UserVmVO> sc = IdsSearch.create();
         sc.setParameters("ids", ids.toArray());
         return listBy(sc);