server: NPE may cause management server to not start (#5001)

This NPE may happen when a VM is marked removed in the DB but not its
nics on a shared network. This can usually happen due to a failed
expunged VM or when an admin manually marks a VM as removed in DB but
does not cleanup the nics/network resources.

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>

Author: yadvr

server/src/main/java/com/cloud/vm/UserVmManagerImpl.java

@@ -2232,7 +2232,7 @@ private void loadVmDetailsInMapForExternalDhcpIp() {
                         VMInstanceVO vmInstance = _vmInstanceDao.findById(vmId);
 
                         // only load running vms. For stopped vms get loaded on starting
-                        if (vmInstance.getState() == State.Running) {
+                        if (vmInstance != null && vmInstance.getState() == State.Running) {
                             VmAndCountDetails vmAndCount = new VmAndCountDetails(vmId, VmIpFetchTrialMax.value());
                             vmIdCountMap.put(nicId, vmAndCount);
                         }