Prevent NPE on reboot stopped VM and startVM output with null displayname (#6397)

* Prevent NPE on reboot stopped VM

* Use VM UUID instead of VM ID

* Apply suggestion

* Refactor and fix start VM output

* Use format instead of concatenation

Author: nvazquez

engine/schema/src/main/java/com/cloud/vm/UserVmVO.java

@@ -28,6 +28,7 @@
 
 import com.cloud.hypervisor.Hypervisor.HypervisorType;
 import com.cloud.uservm.UserVm;
+import org.apache.commons.lang3.StringUtils;
 
 @Entity
 @Table(name = "user_vm")
@@ -141,4 +142,8 @@ public void setUserVmType(String userVmType) {
     public String getName() {
         return instanceName;
     }
+
+    public String getDisplayNameOrHostName() {
+        return StringUtils.isNotBlank(displayName) ? displayName : getHostName();
+    }
 }

server/src/main/java/com/cloud/api/query/dao/UserVmJoinDaoImpl.java

@@ -127,7 +127,7 @@ public UserVmResponse newUserVmResponse(ResponseView view, String objectName, Us
         userVmResponse.setName(userVm.getName());
 
         if (userVm.getDisplayName() != null) {
-        userVmResponse.setDisplayName(userVm.getDisplayName());
+            userVmResponse.setDisplayName(userVm.getDisplayName());
         } else {
             userVmResponse.setDisplayName(userVm.getName());
         }

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

@@ -3130,6 +3130,11 @@ public UserVm rebootVirtualMachine(RebootVMCmd cmd) throws InsufficientCapacityE
             throw new InvalidParameterValueException("Unable to find a virtual machine with id " + vmId);
         }
 
+        if (vmInstance.getState() != State.Running) {
+            throw new InvalidParameterValueException(String.format("The VM %s (%s) is not running, unable to reboot it",
+                    vmInstance.getUuid(), vmInstance.getDisplayNameOrHostName()));
+        }
+
         _accountMgr.checkAccess(caller, null, true, vmInstance);
 
         checkIfHostOfVMIsInPrepareForMaintenanceState(vmInstance.getHostId(), vmId, "Reboot");
@@ -5119,8 +5124,9 @@ public Pair<UserVmVO, Map<VirtualMachineProfile.Param, Object>> startVirtualMach
             throw new InvalidParameterValueException("unable to find a virtual machine with id " + vmId);
         }
 
-        if (vm.getState()== State.Running) {
-            throw new InvalidParameterValueException("The virtual machine "+ vm.getUuid()+ " ("+ vm.getDisplayName()+ ") is already running");
+        if (vm.getState() == State.Running) {
+            throw new InvalidParameterValueException(String.format("The virtual machine %s (%s) is already running",
+                    vm.getUuid(), vm.getDisplayNameOrHostName()));
         }
 
         _accountMgr.checkAccess(callerAccount, null, true, vm);