Created Issue: System.NullReferenceException with MSBuild.ExtensionPack.Tfs.DevEnv [10426]

I am using MSBuild.ExtensionPack.Tfs.DevEnv 3.5.7.0 in my MSBuild script. I got the follwing error:
Using "MSBuild.ExtensionPack.Tfs.DevEnv" task from assembly "C:\Program Files (x86)\MSBuild\ExtensionPack\\MSBuild.ExtensionPack.Tfs.dll".
Task "MSBuild.ExtensionPack.Tfs.DevEnv" (TaskId:563)
error MSB4018: The "MSBuild.ExtensionPack.Tfs.DevEnv" task failed unexpectedly.
error MSB4018: System.NullReferenceException: Object reference not set to an instance of an object.
error MSB4018: at MSBuild.ExtensionPack.Tfs.DevEnv.Execute() in D:\Projects\MSBuildExtensionPack\Releases\3.5.7.0\Main3.5\TFS\DevEnv.cs:line 307
error MSB4018: at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
error MSB4018: at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask, Boolean& taskResult)
Done executing task "MSBuild.ExtensionPack.Tfs.DevEnv" -- FAILED. (TaskId:563)
Done building target "AfterCompile" in project "TFSBuild.proj" -- FAILED.: (TargetId:796)

My build script has the following:
<Import Project="$(MSBuildExtensionsPath)\ExtensionPack\MSBuild.ExtensionPack.tasks"/>
<MSBuild.ExtensionPack.Tfs.DevEnv TeamFoundationServerUrl="$(TeamFoundationServerUrl)" BuildUri="$(BuildUri)" Solution="$(SolutionRoot)\%(InstallerFile.Identity)" SolutionConfiguration="$(Config)" SolutionPlatform="" Target="Build" Version="10" />

In the build log:
DevEnvDir = *Undefined*

Does this have anything to do with this error?

Thank you