MSBuildWorkspace.OpenSolutionAsync引发异常

以下是完整的代码：

MSBuildWorkspace msBuild = MSBuildWorkspace.Create();
Solution sln = await msBuild.OpenSolutionAsync(solutionPath);//NullReferenceException

其中solutionPath是有效的.slnVisual Studio 2015解决方案。我尝试了一个Winforms新项目和一个带有简单类的dll。我在尝试阅读之前关闭了该解决方案，但这无济于事。它仍然抛出NullReferenceException。我使用的是VS2015。x64 Windows 10。

MSBuildWorkspace是错误的Workspace吗？还有什么东西不见了吗？

_{（NullReferenceException实际上是一个由方法引发的奇怪错误。这通常是由mistakenNull.DoSomething（）；之类的东西引发的错误类型。）}

EDIT 2-此代码位于解决方案的dll项目中，该解决方案还包含一个调用此代码的简单Winforms项目。（因为Roslyn项目模板创建了一个dll项目。）也许这很重要。

编辑-堆栈跟踪

异常：对象引用未设置为对象的实例。

堆栈跟踪：

   at Microsoft.CodeAnalysis.CSharp.CSharpProjectFileLoader.CSharpProjectFile.GetReferences(CSharpCompilerInputs compilerInputs, ProjectInstance executedProject, IEnumerable`1& metadataReferences, IEnumerable`1& analyzerReferences)
   at Microsoft.CodeAnalysis.CSharp.CSharpProjectFileLoader.CSharpProjectFile.CreateProjectFileInfo(CSharpCompilerInputs compilerInputs, ProjectInstance executedProject)
   at Microsoft.CodeAnalysis.CSharp.CSharpProjectFileLoader.CSharpProjectFile.<GetProjectFileInfoAsync>d__7.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at Microsoft.CodeAnalysis.MSBuild.MSBuildWorkspace.<LoadProjectAsync>d__40.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.CodeAnalysis.MSBuild.MSBuildWorkspace.<GetOrLoadProjectAsync>d__39.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.CodeAnalysis.MSBuild.MSBuildWorkspace.<OpenSolutionAsync>d__34.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at namespace1.RosTest.<RenameMethods>d__0.MoveNext() in C:'Users'...