Object reference not set to an instance of an object.

public List<VMInfo> GetAllVirtualMachines()
       {
           List<VMInfo> vmInfoList = new List<VMInfo>();
           GetSCVirtualMachine.ParameterSets.AllSet paramSet = new GetSCVirtualMachine.ParameterSets.AllSet();

           try
           {
               //create the command
               GeneratedCommand<VM> vmCommand = GetSCVirtualMachine.Create(paramSet);
               //Using the PowerShellConext to invoke the cmdlet
               //Since PowerShellContext only provides the asynch call, we need to simulate the synch call here

               IAsyncResult ar = this.PSContext.BeginInvoke<VM>(vmCommand, null, null);
               //We are using AutoResetEvent to block the execution until the cmdlet execution is completed
               ar.AsyncWaitHandle.WaitOne();
               //after the callback, we will continue our execution and retrieve the result back
               InvocationResults<VM> results = this.PSContext.EndInvoke<VM>(ar);
               if (results.Errors.Count == 0)
               {
                   foreach (VM vm in results.Output)
                   {
                       //Using our utility class to build our return object
                       VMInfo vmInfo = DataUtil.GetVMInfo(vm);
                       vmInfoList.Add(vmInfo);
                   }
               }
               else
               {
                   StringBuilder errorMsg = new StringBuilder("Failed to get VMs: ");
                   foreach (ErrorInfo error in results.Errors)
                   {
                       errorMsg.AppendLine(error.Problem + " " + error.RecommendedAction);
                   }

                   throw new HostingManagementException(errorMsg.ToString());
               }

           }
           catch (Exception ex)
           {
               throw new HostingManagementException(string.Format(ErrorMessages.VMMManager_GetAllVirtualMachines_Failed_to_retrieve_all_virtual_machines, ex.Message), ex);
           }
           return vmInfoList;
       }