azure-pipelines-tasks: Hi, Run functional test failing with an exception while unregistering the agent

after finishing the test agent deployment whenever it try to run tests following this comes in log

2017-04-05T23:45:37.2174502Z DistributedTests: Test configuration ID: 7

10 2017-04-05T23:45:39.0925200Z DistributedTests: Trying to unregister TestAgents from Test Machines

11 2017-04-05T23:45:39.0955208Z DistributedTests: Task ‘UnRegisterAgent’ on machine ‘KRKAUTOQA.branddevelopers.co.nz:5985’ is being run

12 2017-04-05T23:45:44.8007294Z DistributedTests: Task ‘UnRegisterAgent’ on machine ‘KRKAUTOQA.branddevelopers.co.nz:5985’ completed.

13 2017-04-05T23:45:44.8017303Z DistributedTests: Trying to unregister TestAgent from Application Under Test Machines

14 2017-04-05T23:45:44.8037311Z ##[warning]For troubleshooting, refer https://aka.ms/remotevstest.

15 2017-04-05T23:45:44.8137386Z ##[error]System.NullReferenceException: Object reference not set to an instance of an object.

16 2017-04-05T23:45:44.8147395Z ##[error] at Microsoft.TeamFoundation.DistributedTask.Task.DistributedTestAutomation.DtlMachineDeploymentHelper.UnregisterAgents(String unConfigureTestAgentScriptPath)

17 2017-04-05T23:45:44.8147395Z ##[error] at Microsoft.TeamFoundation.DistributedTask.Task.DistributedTestAutomation.RunTests.Run()

18 2017-04-05T23:45:44.8157403Z ##[error] at Microsoft.TeamFoundation.DistributedTask.Task.DistributedTestAutomation.TaskRunner.Run(Dictionary`2 arguments, VssConnection connection, TaskType taskType)

19 2017-04-05T23:45:44.8167403Z ##[error] at Microsoft.TeamFoundation.DistributedTask.Task.DistributedTestAutomation.RundistributedTestsCmdLet.ProcessRecord()

Also the DTA Execution logs are below

I, 2008, 1, 2017/04/06, 13:44:25.610, 23341756674, DTAExecutionHost.exe, Main.TryReadAndCacheVssCredentials Acquiring the Token Info I, 2008, 1, 2017/04/06, 13:44:25.746, 23343090374, DTAExecutionHost.exe, Communicating to the Token Servicehttps://bdltfs.visualstudio.com W, 2008, 1, 2017/04/06, 13:44:25.832, 23343952009, DTAExecutionHost.exe, Service task failed. Retry attempt 10. I, 8172, 1, 2017/04/06, 13:44:30.691, 23392553221, DTAExecutionHost.exe, Main.TryReadAndCacheVssCredentials Acquiring the Token Info I, 8172, 1, 2017/04/06, 13:44:30.821, 23393830008, DTAExecutionHost.exe, Communicating to the Token Servicehttps://bdltfs.visualstudio.com I, 8172, 1, 2017/04/06, 13:44:30.913, 23394747459, DTAExecutionHost.exe, Closing the Token Service I, 8172, 1, 2017/04/06, 13:44:31.142, KRKAUTOQA\DTAExecutionHost, ExecutionTaskStateModel.GetExecutionAdapter : Initializing VstestAdapter. I, 8172, 1, 2017/04/06, 13:44:31.144, KRKAUTOQA\DTAExecutionHost, ExecutionTaskStateModel.Start : Starting to monitor tasks V, 8172, 1, 2017/04/06, 13:44:31.149, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : Getting Command for Test Agent Microsoft.TeamFoundation.Test.WebApi.TestAgent Web method running: [https://bdltfs.visualstudio.com/_apis/test/Agents/152/Commands/0] (GET)0[test] I, 8172, 1, 2017/04/06, 13:44:31.213, 23397753997, DTAExecutionHost.exe, ******************************************************************** I, 8172, 1, 2017/04/06, 13:44:31.213, 23397754762, DTAExecutionHost.exe, Main.InitializeAndStartExecutionHost. ExecutionHost has been started Web method response: [https://bdltfs.visualstudio.com/_apis/test/Agents/152/Commands/0] (GET)0[test] 372 ms V, 8172, 8, 2017/04/06, 13:44:31.780, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener:DispatchAsync W, 8172, 8, 2017/04/06, 13:44:31.784, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : TestExecutionCommand received with None. Retrying it. W, 8172, 8, 2017/04/06, 13:44:31.784, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : Queue not found. Delaying for 3000 milliseconds. V, 8172, 4, 2017/04/06, 13:44:34.784, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : Getting Command for Test Agent Microsoft.TeamFoundation.Test.WebApi.TestAgent Web method running: [https://bdltfs.visualstudio.com/_apis/test/Agents/152/Commands/0] (GET)0[test] Web method response: [https://bdltfs.visualstudio.com/_apis/test/Agents/152/Commands/0] (GET)0[test] 37 ms V, 8172, 10, 2017/04/06, 13:44:34.822, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener:DispatchAsync W, 8172, 10, 2017/04/06, 13:44:34.822, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : TestExecutionCommand received with None. Retrying it. W, 8172, 10, 2017/04/06, 13:44:34.823, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : Queue not found. Delaying for 9000 milliseconds. V, 8172, 11, 2017/04/06, 13:44:43.823, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : Getting Command for Test Agent Microsoft.TeamFoundation.Test.WebApi.TestAgent Web method running: [https://bdltfs.visualstudio.com/_apis/test/Agents/152/Commands/0] (GET)0[test] Web method response: [https://bdltfs.visualstudio.com/_apis/test/Agents/152/Commands/0] (GET)0[test] 35 ms V, 8172, 8, 2017/04/06, 13:44:43.859, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener:DispatchAsync W, 8172, 8, 2017/04/06, 13:44:43.859, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : TestExecutionCommand received with None. Retrying it. W, 8172, 8, 2017/04/06, 13:44:43.859, KRKAUTOQA\DTAExecutionHost, TestExecutionServiceCommandQueueListener.DispatchAsync : Queue not found. Delaying for 27000 milliseconds.