这些函数定义不相同吗?

PowerShell 4.0

它工作得很好:

$cad  = [Autodesk.AutoCAD.ApplicationServices.Application]
function Get-DocumentManager { $cad::DocumentManager }
function Get-CurrentDocument { $cad::DocumentManager.MdiActiveDocument }
function Get-CurrentEditor { (Get-CurrentDocument).Editor }
function Get-CurrentDatabase { (Get-CurrentDocument).Database }

所有这些函数都返回必要的对象。但如果我重写 Get-CurrentDocument 函数,然后我得到问题:

$cad  = [Autodesk.AutoCAD.ApplicationServices.Application]
function Get-DocumentManager { $cad::DocumentManager }
function Get-CurrentDocument { (Get-DocumentManager).MdiActiveDocument }
function Get-CurrentEditor { (Get-CurrentDocument).Editor }
function Get-CurrentDatabase { (Get-CurrentDocument).Database }

当我启动 获取当前文档 功能:

对象引用未设置为对象的实例。

为什么会发生这种情况?这种方式很适合我 Get-CurrentEditor 和 Get-CurrentDatabase 功能。